| Age | Commit message (Collapse) | Author | Files | Lines |
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Export fscache_put_volume() and add fscache_try_get_volume()
helper function to allow cachefiles to get/put fscache_volume
via linux/fscache-cache.h.
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Link: https://lore.kernel.org/r/20240628062930.2467993-2-libaokun@huaweicloud.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
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An issue can occur between write-streaming (storing dirty data in partial
non-uptodate pages) and a cachefiles object being culled to make space.
The problem occurs because the cache object is only marked in use while
there are files open using it. Once it has been released, it can be culled
and the cookie marked disabled.
At this point, a streaming write is permitted to occur (if the cache is
active, we require pages to be prefetched and cached), but the cache can
become active again before this gets flushed out - and then two effects can
occur:
(1) The cache may be asked to write out a region that's less than its DIO
block size (assumed by cachefiles to be PAGE_SIZE) - and this causes
one of two debugging statements to be emitted.
(2) netfs_how_to_modify() gets confused because it sees a page that isn't
allowed to be non-uptodate being uptodate and tries to prefetch it -
leading to a warning that PG_fscache is set twice.
Fix this by the following means:
(1) Add a netfs_inode flag to disallow write-streaming to an inode and set
it if we ever do local caching of that inode. It remains set for the
lifetime of that inode - even if the cookie becomes disabled.
(2) If the no-write-streaming flag is set, then make netfs_how_to_modify()
always want to prefetch instead.
(3) If netfs_how_to_modify() decides it wants to prefetch a folio, but
that folio has write-streamed data in it, then it requires the folio
be flushed first.
(4) Export a counter of the number of times we wanted to prefetch a
non-uptodate page, but found it had write-streamed data in it.
(5) Export a counter of the number of times we cancelled a write to the
cache because it didn't DIO align and remove the debug statements.
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-erofs@lists.ozlabs.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
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Add a stat counter of culling events whereby the cache backend culls a file
to make space (when asked by cachefilesd in this case) and display in
/proc/fs/fscache/stats.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819654165.215744.3797804661644212436.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906961387.143852.9291157239960289090.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967168266.1823006.14436200166581605746.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021567619.640689.4339228906248763197.stgit@warthog.procyon.org.uk/ # v4
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Add stat counters of no-space events that caused caching not to happen and
display in /proc/fs/fscache/stats.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819653216.215744.17210522251617386509.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906958369.143852.7257100711818401748.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967166917.1823006.14842444049198947892.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021566184.640689.4417328329632709265.stgit@warthog.procyon.org.uk/ # v4
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Provide a function to change the size of the storage attached to a cookie,
to match the size of the file being cached when it's changed by truncate or
fallocate:
void fscache_resize_cookie(struct fscache_cookie *cookie,
loff_t new_size);
This acts synchronously and is expected to run under the inode lock of the
caller.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819621839.215744.7895597119803515402.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906922387.143852.16394459879816147793.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967128998.1823006.10740669081985775576.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021527861.640689.3466382085497236267.stgit@warthog.procyon.org.uk/ # v4
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Provide read/write stat counters for the cache backend to use.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819609532.215744.10821082637727410554.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906912598.143852.12960327989649429069.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967113830.1823006.3222957649202368162.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021517502.640689.6077928311710357342.stgit@warthog.procyon.org.uk/ # v4
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Count the data storage objects that are currently allocated in a cache.
This is used to pin certain cache structures until cache withdrawal is
complete.
Three helpers are provided to manage and make use of the count:
(1) void fscache_count_object(struct fscache_cache *cache);
This should be called by the cache backend to note that an object has
been allocated and attached to the cache.
(2) void fscache_uncount_object(struct fscache_cache *cache);
This should be called by the backend to note that an object has been
destroyed. This sends a wakeup event that allows cache withdrawal to
proceed if it was waiting for that object.
(3) void fscache_wait_for_objects(struct fscache_cache *cache);
This can be used by the backend to wait for all outstanding cache
object to be destroyed.
Each cache's counter is displayed as part of /proc/fs/fscache/caches.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819608594.215744.1812706538117388252.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906911646.143852.168184059935530127.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967111846.1823006.9868154941573671255.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021516219.640689.4934796654308958158.stgit@warthog.procyon.org.uk/ # v4
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Provide a function to begin a read operation:
int fscache_begin_read_operation(
struct netfs_cache_resources *cres,
struct fscache_cookie *cookie)
This is primarily intended to be called by network filesystems on behalf of
netfslib, but may also be called to use the I/O access functions directly.
It attaches the resources required by the cache to cres struct from the
supplied cookie.
This holds access to the cache behind the cookie for the duration of the
operation and forces cache withdrawal and cookie invalidation to perform
synchronisation on the operation. cres->inval_counter is set from the
cookie at this point so that it can be compared at the end of the
operation.
Note that this does not guarantee that the cache state is fully set up and
able to perform I/O immediately; looking up and creation may be left in
progress in the background. The operations intended to be called by the
network filesystem, such as reading and writing, are expected to wait for
the cookie to move to the correct state.
This will, however, potentially sleep, waiting for a certain minimum state
to be set or for operations such as invalidate to advance far enough that
I/O can resume.
Also provide a function for the cache to call to wait for the cache object
to get to a state where it can be used for certain things:
bool fscache_wait_for_operation(struct netfs_cache_resources *cres,
enum fscache_want_stage stage);
This looks at the cache resources provided by the begin function and waits
for them to get to an appropriate stage. There's a choice of wanting just
some parameters (FSCACHE_WANT_PARAM) or the ability to do I/O
(FSCACHE_WANT_READ or FSCACHE_WANT_WRITE).
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819603692.215744.146724961588817028.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906910672.143852.13856103384424986357.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967110245.1823006.2239170567540431836.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021513617.640689.16627329360866150606.stgit@warthog.procyon.org.uk/ # v4
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Add a function to invalidate the cache behind a cookie:
void fscache_invalidate(struct fscache_cookie *cookie,
const void *aux_data,
loff_t size,
unsigned int flags)
This causes any cached data for the specified cookie to be discarded. If
the cookie is marked as being in use, a new cache object will be created if
possible and future I/O will use that instead. In-flight I/O should be
abandoned (writes) or reconsidered (reads). Each time it is called
cookie->inval_counter is incremented and this can be used to detect
invalidation at the end of an I/O operation.
The coherency data attached to the cookie can be updated and the cookie
size should be reset. One flag is available, FSCACHE_INVAL_DIO_WRITE,
which should be used to indicate invalidation due to a DIO write on a
file. This will temporarily disable caching for this cookie.
Changes
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ver #2:
- Should only change to inval state if can get access to cache.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819602231.215744.11206598147269491575.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906909707.143852.18056070560477964891.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967107447.1823006.5945029409592119962.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021512640.640689.11418616313147754172.stgit@warthog.procyon.org.uk/ # v4
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Implement a very simple cookie state machine to handle lookup,
invalidation, withdrawal, relinquishment and, to be added later, commit on
LRU discard.
Three cache methods are provided: ->lookup_cookie() to look up and, if
necessary, create a data storage object; ->withdraw_cookie() to free the
resources associated with that object and potentially delete it; and
->prepare_to_write(), to do prepare for changes to the cached data to be
modified locally.
Changes
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ver #3:
- Fix a race between LRU discard and relinquishment whereby the former
would override the latter and thus the latter would never happen[1].
ver #2:
- Don't hold n_accesses elevated whilst cache is bound to a cookie, but
rather add a flag that prevents the state machine from being queued when
n_accesses reaches 0.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/599331.1639410068@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/r/163819599657.215744.15799615296912341745.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906903925.143852.1805855338154353867.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967105456.1823006.14730395299835841776.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021510706.640689.7961423370243272583.stgit@warthog.procyon.org.uk/ # v4
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Add a function to the backend API to note an I/O error in a cache.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819598741.215744.891281275151382095.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906901316.143852.15225412215771586528.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967100721.1823006.16435671567428949398.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021508840.640689.11902836226570620424.stgit@warthog.procyon.org.uk/ # v4
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Add cache methods to lookup, create and remove a volume.
Looking up or creating the volume requires the cache pinning for access;
freeing the volume requires the volume pinning for access. The
->acquire_volume() method is used to ask the cache backend to lookup and,
if necessary, create a volume; the ->free_volume() method is used to free
the resources for a volume.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819597821.215744.5225318658134989949.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906898645.143852.8537799955945956818.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967099771.1823006.1455197910571061835.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021507345.640689.4073511598838843040.stgit@warthog.procyon.org.uk/ # v4
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Implement functions to allow the cache backend to add or remove a cache:
(1) Declare a cache to be live:
int fscache_add_cache(struct fscache_cache *cache,
const struct fscache_cache_ops *ops,
void *cache_priv);
Take a previously acquired cache cookie, set the operations table and
private data and mark the cache open for access.
(2) Withdraw a cache from service:
void fscache_withdraw_cache(struct fscache_cache *cache);
This marks the cache as withdrawn and thus prevents further
cache-level and volume-level accesses.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819596022.215744.8799712491432238827.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906896599.143852.17049208999019262884.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967097870.1823006.3470041000971522030.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021505541.640689.1819714759326331054.stgit@warthog.procyon.org.uk/ # v4
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Add a number of helper functions to manage access to a cookie, pinning the
cache object in place for the duration to prevent cache withdrawal from
removing it:
(1) void fscache_init_access_gate(struct fscache_cookie *cookie);
This function initialises the access count when a cache binds to a
cookie. An extra ref is taken on the access count to prevent wakeups
while the cache is active. We're only interested in the wakeup when a
cookie is being withdrawn and we're waiting for it to quiesce - at
which point the counter will be decremented before the wait.
The FSCACHE_COOKIE_NACC_ELEVATED flag is set on the cookie to keep
track of the extra ref in order to handle a race between
relinquishment and withdrawal both trying to drop the extra ref.
(2) bool fscache_begin_cookie_access(struct fscache_cookie *cookie,
enum fscache_access_trace why);
This function attempts to begin access upon a cookie, pinning it in
place if it's cached. If successful, it returns true and leaves a the
access count incremented.
(3) void fscache_end_cookie_access(struct fscache_cookie *cookie,
enum fscache_access_trace why);
This function drops the access count obtained by (2), permitting
object withdrawal to take place when it reaches zero.
A tracepoint is provided to track changes to the access counter on a
cookie.
Changes
=======
ver #2:
- Don't hold n_accesses elevated whilst cache is bound to a cookie, but
rather add a flag that prevents the state machine from being queued when
n_accesses reaches 0.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819595085.215744.1706073049250505427.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906895313.143852.10141619544149102193.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967095980.1823006.1133648159424418877.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021503063.640689.8870918985269528670.stgit@warthog.procyon.org.uk/ # v4
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Add a pair of helper functions to manage access to a volume, pinning the
volume in place for the duration to prevent cache withdrawal from removing
it:
bool fscache_begin_volume_access(struct fscache_volume *volume,
enum fscache_access_trace why);
void fscache_end_volume_access(struct fscache_volume *volume,
enum fscache_access_trace why);
The way the access gate on the volume works/will work is:
(1) If the cache tests as not live (state is not FSCACHE_CACHE_IS_ACTIVE),
then we return false to indicate access was not permitted.
(2) If the cache tests as live, then we increment the volume's n_accesses
count and then recheck the cache liveness, ending the access if it
ceased to be live.
(3) When we end the access, we decrement the volume's n_accesses and wake
up the any waiters if it reaches 0.
(4) Whilst the cache is caching, the volume's n_accesses is kept
artificially incremented to prevent wakeups from happening.
(5) When the cache is taken offline, the state is changed to prevent new
accesses, the volume's n_accesses is decremented and we wait for it to
become 0.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819594158.215744.8285859817391683254.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906894315.143852.5454793807544710479.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967095028.1823006.9173132503876627466.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021501546.640689.9631510472149608443.stgit@warthog.procyon.org.uk/ # v4
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Add functions to the fscache API to allow data file cookies to be acquired
and relinquished by the network filesystem. It is intended that the
filesystem will create such cookies per-inode under a volume.
To request a cookie, the filesystem should call:
struct fscache_cookie *
fscache_acquire_cookie(struct fscache_volume *volume,
u8 advice,
const void *index_key,
size_t index_key_len,
const void *aux_data,
size_t aux_data_len,
loff_t object_size)
The filesystem must first have created a volume cookie, which is passed in
here. If it passes in NULL then the function will just return a NULL
cookie.
A binary key should be passed in index_key and is of size index_key_len.
This is saved in the cookie and is used to locate the associated data in
the cache.
A coherency data buffer of size aux_data_len will be allocated and
initialised from the buffer pointed to by aux_data. This is used to
validate cache objects when they're opened and is stored on disk with them
when they're committed. The data is stored in the cookie and will be
updateable by various functions in later patches.
The object_size must also be given. This is also used to perform a
coherency check and to size the backing storage appropriately.
This function disallows a cookie from being acquired twice in parallel,
though it will cause the second user to wait if the first is busy
relinquishing its cookie.
When a network filesystem has finished with a cookie, it should call:
void
fscache_relinquish_cookie(struct fscache_volume *volume,
bool retire)
If retire is true, any backing data will be discarded immediately.
Changes
=======
ver #3:
- fscache_hash()'s size parameter is now in bytes. Use __le32 as the unit
to round up to.
- When comparing cookies, simply see if the attributes are the same rather
than subtracting them to produce a strcmp-style return[1].
- Add a check to see if the cookie is still hashed at the point of
freeing.
ver #2:
- Don't hold n_accesses elevated whilst cache is bound to a cookie, but
rather add a flag that prevents the state machine from being queued when
n_accesses reaches 0.
- Remove the unused cookie pointer field from the fscache_acquire
tracepoint.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/CAHk-=whtkzB446+hX0zdLsdcUJsJ=8_-0S1mE_R+YurThfUbLA@mail.gmail.com/ [1]
Link: https://lore.kernel.org/r/163819590658.215744.14934902514281054323.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906891983.143852.6219772337558577395.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967088507.1823006.12659006350221417165.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021498432.640689.12743483856927722772.stgit@warthog.procyon.org.uk/ # v4
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Implement a register of caches and provide functions to manage it.
Two functions are provided for the cache backend to use:
(1) Acquire a cache cookie:
struct fscache_cache *fscache_acquire_cache(const char *name)
This gets the cache cookie for a cache of the specified name and moves
it to the preparation state. If a nameless cache cookie exists, that
will be given this name and used.
(2) Relinquish a cache cookie:
void fscache_relinquish_cache(struct fscache_cache *cache);
This relinquishes a cache cookie, cleans it and makes it available if
it's still referenced by a network filesystem.
Note that network filesystems don't deal with cache cookies directly, but
rather go straight to the volume registration.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819587157.215744.13523139317322503286.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906889665.143852.10378009165231294456.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967085081.1823006.2218944206363626210.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021494847.640689.10109692261640524343.stgit@warthog.procyon.org.uk/ # v4
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Introduce basic skeleton of the new, rewritten fscache driver.
Changes
=======
ver #3:
- Use remove_proc_subtree(), not remove_proc_entry() to remove a populated
dir.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819584034.215744.4290533472390439030.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906887770.143852.3577888294989185666.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967080039.1823006.5702921801104057922.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021491014.640689.4292699878317589512.stgit@warthog.procyon.org.uk/ # v4
|
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Remove the code that comprises the fscache driver as it's going to be
substantially rewritten, with the majority of the code being erased in the
rewrite.
A small piece of linux/fscache.h is left as that is #included by a bunch of
network filesystems.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819578724.215744.18210619052245724238.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906884814.143852.6727245089843862889.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967077097.1823006.1377665951499979089.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021485548.640689.13876080567388696162.stgit@warthog.procyon.org.uk/ # v4
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Remove the object list procfile from fscache as objects will become
entirely internal to the cache.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/162431198332.2908479.5847286163455099669.stgit@warthog.procyon.org.uk/
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Remove the histogram stuff as it's mostly going to be outdated.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/162431195953.2908479.16770977195634296638.stgit@warthog.procyon.org.uk/
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Add an alternate API by which the cache can be accessed through a kiocb,
doing async DIO, rather than using the current API that tells the cache
where all the pages are.
The new API is intended to be used in conjunction with the netfs helper
library. A filesystem must pick one or the other and not mix them.
Filesystems wanting to use the new API must #define FSCACHE_USE_NEW_IO_API
before #including the header. This prevents them from continuing to use
the old API at the same time as there are incompatibilities in how the
PG_fscache page bit is used.
Changes:
v6:
- Provide a routine to shape a write so that the start and length can be
aligned for DIO[3].
v4:
- Use the vfs_iocb_iter_read/write() helpers[1]
- Move initial definition of fscache_begin_read_operation() here.
- Remove a commented-out line[2]
- Combine ki->term_func calls in cachefiles_read_complete()[2].
- Remove explicit NULL initialiser[2].
- Remove extern on func decl[2].
- Put in param names on func decl[2].
- Remove redundant else[2].
- Fill out the kdoc comment for fscache_begin_read_operation().
- Rename fs/fscache/page2.c to io.c to match later patches.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-and-tested-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Dave Wysochanski <dwysocha@redhat.com>
Tested-By: Marc Dionne <marc.dionne@auristor.com>
cc: Christoph Hellwig <hch@lst.de>
cc: linux-cachefs@redhat.com
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: v9fs-developer@lists.sourceforge.net
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20210216102614.GA27555@lst.de/ [1]
Link: https://lore.kernel.org/r/20210216084230.GA23669@lst.de/ [2]
Link: https://lore.kernel.org/r/161781047695.463527.7463536103593997492.stgit@warthog.procyon.org.uk/ [3]
Link: https://lore.kernel.org/r/161118142558.1232039.17993829899588971439.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161161037850.2537118.8819808229350326503.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161340402057.1303470.8038373593844486698.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/161539545919.286939.14573472672781434757.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/161653801477.2770958.10543270629064934227.stgit@warthog.procyon.org.uk/ # v5
Link: https://lore.kernel.org/r/161789084517.6155.12799689829859169640.stgit@warthog.procyon.org.uk/ # v6
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There is a regular need in the kernel to provide a way to declare having a
dynamically sized set of trailing elements in a structure. Kernel code should
always use “flexible array members”[1] for these cases. The older style of
one-element or zero-length arrays should no longer be used[2].
[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://github.com/KSPP/linux/issues/21
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
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- Add a SPDX header;
- Adjust document and section titles;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add table markups;
- Add it to filesystems/caching/index.rst.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/5d0a61abaa87bfe913b9e2f321e74ef7af0f3dfc.1588021877.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Based on 1 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-or-later
has been chosen to replace the boilerplate/reference in 3029 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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The code in fscache_retrieval_complete is using atomic_sub followed by an
atomic_read:
atomic_sub(n_pages, &op->n_pages);
if (atomic_read(&op->n_pages) <= 0)
fscache_op_complete(&op->op, true);
This causes two threads doing a decrement of n_pages to race with each
other seeing the op->refcount 0 at same time - and they end up calling
fscache_op_complete() in both the threads leading to an assertion failure.
Fix this by using atomic_sub_return_relaxed() instead of two calls. Note
that I'm using 'relaxed' rather than, say, 'release' as there aren't
multiple variables that appear to need ordering across the release.
The oops looks something like:
FS-Cache: Assertion failed
FS-Cache: 0 > 0 is false
...
kernel BUG at /usr/src/linux-4.4.0/fs/fscache/operation.c:449!
...
Workqueue: fscache_operation fscache_op_work_func [fscache]
...
RIP: 0010:[<ffffffffc037eacd>] fscache_op_complete+0x10d/0x180 [fscache]
...
Call Trace:
[<ffffffffc1464cf9>] cachefiles_read_copier+0x3a9/0x410 [cachefiles]
[<ffffffffc037e272>] fscache_op_work_func+0x22/0x50 [fscache]
[<ffffffff81096da0>] process_one_work+0x150/0x3f0
[<ffffffff8109751a>] worker_thread+0x11a/0x470
[<ffffffff81808e59>] ? __schedule+0x359/0x980
[<ffffffff81097400>] ? rescuer_thread+0x310/0x310
[<ffffffff8109cdd6>] kthread+0xd6/0xf0
[<ffffffff8109cd00>] ? kthread_park+0x60/0x60
[<ffffffff8180d0cf>] ret_from_fork+0x3f/0x70
[<ffffffff8109cd00>] ? kthread_park+0x60/0x60
This seen this in 4.4.x kernels and the same bug affects fscache in latest
upstreams kernels.
Fixes: 1bb4b7f98f36 ("FS-Cache: The retrieval remaining-pages counter needs to be atomic_t")
Signed-off-by: Kiran Kumar Modukuri <kiran.modukuri@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
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Pass the object size in to fscache_acquire_cookie() and
fscache_write_page() rather than the netfs providing a callback by which it
can be received. This makes it easier to update the size of the object
when a new page is written that extends the object.
The current object size is also passed by fscache to the check_aux
function, obviating the need to store it in the aux data.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Anna Schumaker <anna.schumaker@netapp.com>
Tested-by: Steve Dickson <steved@redhat.com>
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Add more tracepoints to fscache, including:
(*) fscache_page - Tracks netfs pages known to fscache.
(*) fscache_check_page - Tracks the netfs querying whether a page is
pending storage.
(*) fscache_wake_cookie - Tracks cookies being woken up after a page
completes/aborts storage in the cache.
(*) fscache_op - Tracks operations being initialised.
(*) fscache_wrote_page - Tracks return of the backend write_page op.
(*) fscache_gang_lookup - Tracks lookup of pages to be stored in the write
operation.
Signed-off-by: David Howells <dhowells@redhat.com>
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Add some tracepoints to fscache:
(*) fscache_cookie - Tracks a cookie's usage count.
(*) fscache_netfs - Logs registration of a network filesystem, including
the pointer to the cookie allocated.
(*) fscache_acquire - Logs cookie acquisition.
(*) fscache_relinquish - Logs cookie relinquishment.
(*) fscache_enable - Logs enablement of a cookie.
(*) fscache_disable - Logs disablement of a cookie.
(*) fscache_osm - Tracks execution of states in the object state machine.
and cachefiles:
(*) cachefiles_ref - Tracks a cachefiles object's usage count.
(*) cachefiles_lookup - Logs result of lookup_one_len().
(*) cachefiles_mkdir - Logs result of vfs_mkdir().
(*) cachefiles_create - Logs result of vfs_create().
(*) cachefiles_unlink - Logs calls to vfs_unlink().
(*) cachefiles_rename - Logs calls to vfs_rename().
(*) cachefiles_mark_active - Logs an object becoming active.
(*) cachefiles_wait_active - Logs a wait for an old object to be
destroyed.
(*) cachefiles_mark_inactive - Logs an object becoming inactive.
(*) cachefiles_mark_buried - Logs the burial of an object.
Signed-off-by: David Howells <dhowells@redhat.com>
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The last parameter to fscache_op_complete() is a bool indicating whether or
not the operation was cancelled. A lot of the time the inverse value is
given or no differentiation is made. Fix this.
Signed-off-by: David Howells <dhowells@redhat.com>
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wait_var_event() API
The old wait_on_atomic_t() is going to get removed, use the more
flexible wait_var_event() API instead.
No change in functionality.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Under some circumstances, an fscache object can become queued such that it
fscache_object_work_func() can be called once the object is in the
OBJECT_DEAD state. This results in the kernel oopsing when it tries to
invoke the handler for the state (which is hard coded to 0x2).
The way this comes about is something like the following:
(1) The object dispatcher is processing a work state for an object. This
is done in workqueue context.
(2) An out-of-band event comes in that isn't masked, causing the object to
be queued, say EV_KILL.
(3) The object dispatcher finishes processing the current work state on
that object and then sees there's another event to process, so,
without returning to the workqueue core, it processes that event too.
It then follows the chain of events that initiates until we reach
OBJECT_DEAD without going through a wait state (such as
WAIT_FOR_CLEARANCE).
At this point, object->events may be 0, object->event_mask will be 0
and oob_event_mask will be 0.
(4) The object dispatcher returns to the workqueue processor, and in due
course, this sees that the object's work item is still queued and
invokes it again.
(5) The current state is a work state (OBJECT_DEAD), so the dispatcher
jumps to it - resulting in an OOPS.
When I'm seeing this, the work state in (1) appears to have been either
LOOK_UP_OBJECT or CREATE_OBJECT (object->oob_table is
fscache_osm_lookup_oob).
The window for (2) is very small:
(A) object->event_mask is cleared whilst the event dispatch process is
underway - though there's no memory barrier to force this to the top
of the function.
The window, therefore is from the time the object was selected by the
workqueue processor and made requeueable to the time the mask was
cleared.
(B) fscache_raise_event() will only queue the object if it manages to set
the event bit and the corresponding event_mask bit was set.
The enqueuement is then deferred slightly whilst we get a ref on the
object and get the per-CPU variable for workqueue congestion. This
slight deferral slightly increases the probability by allowing extra
time for the workqueue to make the item requeueable.
Handle this by giving the dead state a processor function and checking the
for the dead state address rather than seeing if the processor function is
address 0x2. The dead state processor function can then set a flag to
indicate that it's occurred and give a warning if it occurs more than once
per object.
If this race occurs, an oops similar to the following is seen (note the RIP
value):
BUG: unable to handle kernel NULL pointer dereference at 0000000000000002
IP: [<0000000000000002>] 0x1
PGD 0
Oops: 0010 [#1] SMP
Modules linked in: ...
CPU: 17 PID: 16077 Comm: kworker/u48:9 Not tainted 3.10.0-327.18.2.el7.x86_64 #1
Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 12/27/2015
Workqueue: fscache_object fscache_object_work_func [fscache]
task: ffff880302b63980 ti: ffff880717544000 task.ti: ffff880717544000
RIP: 0010:[<0000000000000002>] [<0000000000000002>] 0x1
RSP: 0018:ffff880717547df8 EFLAGS: 00010202
RAX: ffffffffa0368640 RBX: ffff880edf7a4480 RCX: dead000000200200
RDX: 0000000000000002 RSI: 00000000ffffffff RDI: ffff880edf7a4480
RBP: ffff880717547e18 R08: 0000000000000000 R09: dfc40a25cb3a4510
R10: dfc40a25cb3a4510 R11: 0000000000000400 R12: 0000000000000000
R13: ffff880edf7a4510 R14: ffff8817f6153400 R15: 0000000000000600
FS: 0000000000000000(0000) GS:ffff88181f420000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000002 CR3: 000000000194a000 CR4: 00000000001407e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Stack:
ffffffffa0363695 ffff880edf7a4510 ffff88093f16f900 ffff8817faa4ec00
ffff880717547e60 ffffffff8109d5db 00000000faa4ec18 0000000000000000
ffff8817faa4ec18 ffff88093f16f930 ffff880302b63980 ffff88093f16f900
Call Trace:
[<ffffffffa0363695>] ? fscache_object_work_func+0xa5/0x200 [fscache]
[<ffffffff8109d5db>] process_one_work+0x17b/0x470
[<ffffffff8109e4ac>] worker_thread+0x21c/0x400
[<ffffffff8109e290>] ? rescuer_thread+0x400/0x400
[<ffffffff810a5acf>] kthread+0xcf/0xe0
[<ffffffff810a5a00>] ? kthread_create_on_node+0x140/0x140
[<ffffffff816460d8>] ret_from_fork+0x58/0x90
[<ffffffff810a5a00>] ? kthread_create_on_node+0x140/0x140
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Jeremy McNicoll <jeremymc@redhat.com>
Tested-by: Frank Sorenson <sorenson@redhat.com>
Tested-by: Benjamin Coddington <bcodding@redhat.com>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
|
|
__fscache_check_consistency() calls check_consistency() callback
and return the callback's return value. But the return type of
check_consistency() is bool. So __fscache_check_consistency()
return 1 if the cache is inconsistent. This is inconsistent with
the document.
Signed-off-by: Yan, Zheng <zyan@redhat.com>
Acked-by: David Howells <dhowells@redhat.com>
|
|
Now that the retrieval operation may be disposed of by fscache_put_operation()
before we actually set the context, the retrieval-specific cleanup operation
can produce a NULL-pointer dereference when it tries to unconditionally clean
up the netfs context.
Given that it is expected that we'll get at least as far as the place where we
currently set the context pointer and it is unlikely we'll go through the
error handling paths prior to that point, retain the context right from the
point that the retrieval op is allocated.
Concomitant to this, we need to retain the cookie pointer in the retrieval op
also so that we can call the netfs to release its context in the release
method.
In addition, we might now get into fscache_release_retrieval_op() with the op
only initialised. To this end, set the operation to DEAD only after the
release method has been called and skip the n_pages test upon cleanup if the
op is still in the INITIALISED state.
Without these changes, the following oops might be seen:
BUG: unable to handle kernel NULL pointer dereference at 00000000000000b8
...
RIP: 0010:[<ffffffffa0089c98>] fscache_release_retrieval_op+0xae/0x100
...
Call Trace:
[<ffffffffa0088560>] fscache_put_operation+0x117/0x2e0
[<ffffffffa008b8f5>] __fscache_read_or_alloc_pages+0x351/0x3ac
[<ffffffffa00b761f>] __nfs_readpages_from_fscache+0x59/0xbf [nfs]
[<ffffffffa00b06c5>] nfs_readpages+0x10c/0x185 [nfs]
[<ffffffff81124925>] ? alloc_pages_current+0x119/0x13e
[<ffffffff810ee5fd>] ? __page_cache_alloc+0xfb/0x10a
[<ffffffff810f87f8>] __do_page_cache_readahead+0x188/0x22c
[<ffffffff810f8b3a>] ondemand_readahead+0x29e/0x2af
[<ffffffff810f8c92>] page_cache_sync_readahead+0x38/0x3a
[<ffffffff810ef337>] generic_file_read_iter+0x1a2/0x55a
[<ffffffffa00a9dff>] ? nfs_revalidate_mapping+0xd6/0x288 [nfs]
[<ffffffffa00a6a23>] nfs_file_read+0x49/0x70 [nfs]
[<ffffffff811363be>] new_sync_read+0x78/0x9c
[<ffffffff81137164>] __vfs_read+0x13/0x38
[<ffffffff8113721e>] vfs_read+0x95/0x121
[<ffffffff811372f6>] SyS_read+0x4c/0x8a
[<ffffffff81557a52>] system_call_fastpath+0x12/0x17
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steve Dickson <steved@redhat.com>
Acked-by: Jeff Layton <jeff.layton@primarydata.com>
|
|
Any time an incomplete operation is cancelled, the operation cancellation
function needs to be called to clean up. This is currently being passed
directly to some of the functions that might want to call it, but not all.
Instead, pass the cancellation method pointer to the fscache_operation_init()
and have that cache it in the operation struct. Further, plug in a dummy
cancellation handler if the caller declines to set one as this allows us to
call the function unconditionally (the extra overhead isn't worth bothering
about as we don't expect to be calling this typically).
The cancellation method must thence be called everywhere the CANCELLED state
is set. Note that we call it *before* setting the CANCELLED state such that
the method can use the old state value to guide its operation.
fscache_do_cancel_retrieval() needs moving higher up in the sources so that
the init function can use it now.
Without this, the following oops may be seen:
FS-Cache: Assertion failed
FS-Cache: 3 == 0 is false
------------[ cut here ]------------
kernel BUG at ../fs/fscache/page.c:261!
...
RIP: 0010:[<ffffffffa0089c1b>] fscache_release_retrieval_op+0x77/0x100
[<ffffffffa008853d>] fscache_put_operation+0x114/0x2da
[<ffffffffa008b8c2>] __fscache_read_or_alloc_pages+0x358/0x3b3
[<ffffffffa00b761f>] __nfs_readpages_from_fscache+0x59/0xbf [nfs]
[<ffffffffa00b06c5>] nfs_readpages+0x10c/0x185 [nfs]
[<ffffffff81124925>] ? alloc_pages_current+0x119/0x13e
[<ffffffff810ee5fd>] ? __page_cache_alloc+0xfb/0x10a
[<ffffffff810f87f8>] __do_page_cache_readahead+0x188/0x22c
[<ffffffff810f8b3a>] ondemand_readahead+0x29e/0x2af
[<ffffffff810f8c92>] page_cache_sync_readahead+0x38/0x3a
[<ffffffff810ef337>] generic_file_read_iter+0x1a2/0x55a
[<ffffffffa00a9dff>] ? nfs_revalidate_mapping+0xd6/0x288 [nfs]
[<ffffffffa00a6a23>] nfs_file_read+0x49/0x70 [nfs]
[<ffffffff811363be>] new_sync_read+0x78/0x9c
[<ffffffff81137164>] __vfs_read+0x13/0x38
[<ffffffff8113721e>] vfs_read+0x95/0x121
[<ffffffff811372f6>] SyS_read+0x4c/0x8a
[<ffffffff81557a52>] system_call_fastpath+0x12/0x17
The assertion is showing that the remaining number of pages (n_pages) is not 0
when the operation is being released.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steve Dickson <steved@redhat.com>
Acked-by: Jeff Layton <jeff.layton@primarydata.com>
|
|
Out of line fscache_operation_init() so that it can access internal FS-Cache
features, such as stats, in a later commit.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steve Dickson <steved@redhat.com>
Acked-by: Jeff Layton <jeff.layton@primarydata.com>
|
|
fscache_object_is_dead() returns true only if the object is marked dead and
the cache got an I/O error. This should be a logical OR instead. Since two
of the callers got split up into handling for separate subcases, expand the
other callers and kill the function. This is probably the right thing to do
anyway since one of the subcases isn't about the object at all, but rather
about the cache.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steve Dickson <steved@redhat.com>
Acked-by: Jeff Layton <jeff.layton@primarydata.com>
|
|
When submitting an operation, prefer to cancel the operation immediately
rather than queuing it for later processing if the object is marked as dying
(ie. the object state machine has reached the KILL_OBJECT state).
Whilst we're at it, change the series of related test_bit() calls into a
READ_ONCE() and bitwise-AND operators to reduce the number of load
instructions (test_bit() has a volatile address).
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steve Dickson <steved@redhat.com>
Acked-by: Jeff Layton <jeff.layton@primarydata.com>
|
|
Count the number of objects that get culled by the cache backend and the
number of objects that the cache backend declines to instantiate due to lack
of space in the cache.
These numbers are made available through /proc/fs/fscache/stats
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steve Dickson <steved@redhat.com>
Acked-by: Jeff Layton <jeff.layton@primarydata.com>
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Provide the ability to enable and disable fscache cookies. A disabled cookie
will reject or ignore further requests to:
Acquire a child cookie
Invalidate and update backing objects
Check the consistency of a backing object
Allocate storage for backing page
Read backing pages
Write to backing pages
but still allows:
Checks/waits on the completion of already in-progress objects
Uncaching of pages
Relinquishment of cookies
Two new operations are provided:
(1) Disable a cookie:
void fscache_disable_cookie(struct fscache_cookie *cookie,
bool invalidate);
If the cookie is not already disabled, this locks the cookie against other
dis/enablement ops, marks the cookie as being disabled, discards or
invalidates any backing objects and waits for cessation of activity on any
associated object.
This is a wrapper around a chunk split out of fscache_relinquish_cookie(),
but it reinitialises the cookie such that it can be reenabled.
All possible failures are handled internally. The caller should consider
calling fscache_uncache_all_inode_pages() afterwards to make sure all page
markings are cleared up.
(2) Enable a cookie:
void fscache_enable_cookie(struct fscache_cookie *cookie,
bool (*can_enable)(void *data),
void *data)
If the cookie is not already enabled, this locks the cookie against other
dis/enablement ops, invokes can_enable() and, if the cookie is not an
index cookie, will begin the procedure of acquiring backing objects.
The optional can_enable() function is passed the data argument and returns
a ruling as to whether or not enablement should actually be permitted to
begin.
All possible failures are handled internally. The cookie will only be
marked as enabled if provisional backing objects are allocated.
A later patch will introduce these to NFS. Cookie enablement during nfs_open()
is then contingent on i_writecount <= 0. can_enable() checks for a race
between open(O_RDONLY) and open(O_WRONLY/O_RDWR). This simplifies NFS's cookie
handling and allows us to get rid of open(O_RDONLY) accidentally introducing
caching to an inode that's open for writing already.
One operation has its API modified:
(3) Acquire a cookie.
struct fscache_cookie *fscache_acquire_cookie(
struct fscache_cookie *parent,
const struct fscache_cookie_def *def,
void *netfs_data,
bool enable);
This now has an additional argument that indicates whether the requested
cookie should be enabled by default. It doesn't need the can_enable()
function because the caller must prevent multiple calls for the same netfs
object and it doesn't need to take the enablement lock because no one else
can get at the cookie before this returns.
Signed-off-by: David Howells <dhowells@redhat.com
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Add wrapper functions for dealing with cookie->n_active:
(*) __fscache_use_cookie() to increment it.
(*) __fscache_unuse_cookie() to decrement and test against zero.
(*) __fscache_wake_unused_cookie() to wake up anyone waiting for it to reach
zero.
The second and third are split so that the third can be done after cookie->lock
has been released in case the waiter wakes up whilst we're still holding it and
tries to get it.
We will need to wake-on-zero once the cookie disablement patch is applied
because it will then be possible to see n_active become zero without the cookie
being relinquished.
Also move the cookie usement out of fscache_attr_changed_op() and into
fscache_attr_changed() and the operation struct so that cookie disablement
will be able to track it.
Whilst we're at it, only increment n_active if we're about to do
fscache_submit_op() so that we don't have to deal with undoing it if anything
earlier fails. Possibly this should be moved into fscache_submit_op() which
could look at FSCACHE_OP_UNUSE_COOKIE.
Signed-off-by: David Howells <dhowells@redhat.com>
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Extend the fscache netfs API so that the netfs can ask as to whether a cache
object is up to date with respect to its corresponding netfs object:
int fscache_check_consistency(struct fscache_cookie *cookie)
This will call back to the netfs to check whether the auxiliary data associated
with a cookie is correct. It returns 0 if it is and -ESTALE if it isn't; it
may also return -ENOMEM and -ERESTARTSYS.
The backends now have to implement a mandatory operation pointer:
int (*check_consistency)(struct fscache_object *object)
that corresponds to the above API call. FS-Cache takes care of pinning the
object and the cookie in memory and managing this call with respect to the
object state.
Original-author: Hongyi Jia <jiayisuse@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Hongyi Jia <jiayisuse@gmail.com>
cc: Milosz Tanski <milosz@adfin.com>
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struct fscache_retrieval contains a count of the number of pages that still
need some processing (n_pages). This is decremented as the pages are
processed.
However, this needs to be atomic as fscache_retrieval_complete() (I think) just
occasionally may be called from cachefiles_read_backing_file() and
cachefiles_read_copier() simultaneously.
This happens when an fscache_read_or_alloc_pages() request containing a lot of
pages (say a couple of hundred) is being processed. The read on each backing
page is dispatched individually because we need to insert a monitor into the
waitqueue to catch when the read completes. However, under low-memory
conditions, we might be forced to wait in the allocator - and this gives the
I/O on the backing page a chance to complete first.
When the I/O completes, fscache_enqueue_retrieval() chucks the retrieval onto
the workqueue without waiting for the operation to finish the initial I/O
dispatch (we want to release any pages we can as soon as we can), thus both can
end up running simultaneously and potentially attempting to partially complete
the retrieval simultaneously (ENOMEM may occur, backing pages may already be in
the page cache).
This was demonstrated by parallelling the non-atomic counter with an atomic
counter and printing both of them when the assertion fails. At this point, the
atomic counter has reached zero, but the non-atomic counter has not.
To fix this, make the counter an atomic_t.
This results in the following bug appearing
FS-Cache: Assertion failed
3 == 5 is false
------------[ cut here ]------------
kernel BUG at fs/fscache/operation.c:421!
or
FS-Cache: Assertion failed
3 == 5 is false
------------[ cut here ]------------
kernel BUG at fs/fscache/operation.c:414!
With a backtrace like the following:
RIP: 0010:[<ffffffffa0211b1d>] fscache_put_operation+0x1ad/0x240 [fscache]
Call Trace:
[<ffffffffa0213185>] fscache_retrieval_work+0x55/0x270 [fscache]
[<ffffffffa0213130>] ? fscache_retrieval_work+0x0/0x270 [fscache]
[<ffffffff81090b10>] worker_thread+0x170/0x2a0
[<ffffffff81096d10>] ? autoremove_wake_function+0x0/0x40
[<ffffffff810909a0>] ? worker_thread+0x0/0x2a0
[<ffffffff81096966>] kthread+0x96/0xa0
[<ffffffff8100c0ca>] child_rip+0xa/0x20
[<ffffffff810968d0>] ? kthread+0x0/0xa0
[<ffffffff8100c0c0>] ? child_rip+0x0/0x20
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-and-tested-By: Milosz Tanski <milosz@adfin.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
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Simplify the way fscache cache objects retain their cookie. The way I
implemented the cookie storage handling made synchronisation a pain (ie. the
object state machine can't rely on the cookie actually still being there).
Instead of the the object being detached from the cookie and the cookie being
freed in __fscache_relinquish_cookie(), we defer both operations:
(*) The detachment of the object from the list in the cookie now takes place
in fscache_drop_object() and is thus governed by the object state machine
(fscache_detach_from_cookie() has been removed).
(*) The release of the cookie is now in fscache_object_destroy() - which is
called by the cache backend just before it frees the object.
This means that the fscache_cookie struct is now available to the cache all the
way through from ->alloc_object() to ->drop_object() and ->put_object() -
meaning that it's no longer necessary to take object->lock to guarantee access.
However, __fscache_relinquish_cookie() doesn't wait for the object to go all
the way through to destruction before letting the netfs proceed. That would
massively slow down the netfs. Since __fscache_relinquish_cookie() leaves the
cookie around, in must therefore break all attachments to the netfs - which
includes ->def, ->netfs_data and any outstanding page read/writes.
To handle this, struct fscache_cookie now has an n_active counter:
(1) This starts off initialised to 1.
(2) Any time the cache needs to get at the netfs data, it calls
fscache_use_cookie() to increment it - if it is not zero. If it was zero,
then access is not permitted.
(3) When the cache has finished with the data, it calls fscache_unuse_cookie()
to decrement it. This does a wake-up on it if it reaches 0.
(4) __fscache_relinquish_cookie() decrements n_active and then waits for it to
reach 0. The initialisation to 1 in step (1) ensures that we only get
wake ups when we're trying to get rid of the cookie.
This leaves __fscache_relinquish_cookie() a lot simpler.
***
This fixes a problem in the current code whereby if fscache_invalidate() is
followed sufficiently quickly by fscache_relinquish_cookie() then it is
possible for __fscache_relinquish_cookie() to have detached the cookie from the
object and cleared the pointer before a thread is dispatched to process the
invalidation state in the object state machine.
Since the pending write clearance was deferred to the invalidation state to
make it asynchronous, we need to either wait in relinquishment for the stores
tree to be cleared in the invalidation state or we need to handle the clearance
in relinquishment.
Further, if the relinquishment code does clear the tree, then the invalidation
state need to make the clearance contingent on still having the cookie to hand
(since that's where the tree is rooted) and we have to prevent the cookie from
disappearing for the duration.
This can lead to an oops like the following:
BUG: unable to handle kernel NULL pointer dereference at 000000000000000c
...
RIP: 0010:[<ffffffff8151023e>] _spin_lock+0xe/0x30
...
CR2: 000000000000000c ...
...
Process kslowd002 (...)
....
Call Trace:
[<ffffffffa01c3278>] fscache_invalidate_writes+0x38/0xd0 [fscache]
[<ffffffff810096f0>] ? __switch_to+0xd0/0x320
[<ffffffff8105e759>] ? find_busiest_queue+0x69/0x150
[<ffffffff8110ddd4>] ? slow_work_enqueue+0x104/0x180
[<ffffffffa01c1303>] fscache_object_slow_work_execute+0x5e3/0x9d0 [fscache]
[<ffffffff81096b67>] ? bit_waitqueue+0x17/0xd0
[<ffffffff8110e233>] slow_work_execute+0x233/0x310
[<ffffffff8110e515>] slow_work_thread+0x205/0x360
[<ffffffff81096ca0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff8110e310>] ? slow_work_thread+0x0/0x360
[<ffffffff81096936>] kthread+0x96/0xa0
[<ffffffff8100c0ca>] child_rip+0xa/0x20
[<ffffffff810968a0>] ? kthread+0x0/0xa0
[<ffffffff8100c0c0>] ? child_rip+0x0/0x20
The parameter to fscache_invalidate_writes() was object->cookie which is NULL.
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-By: Milosz Tanski <milosz@adfin.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
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Fix object state machine to have separate work and wait states as that makes
it easier to envision.
There are now three kinds of state:
(1) Work state. This is an execution state. No event processing is performed
by a work state. The function attached to a work state returns a pointer
indicating the next state to which the OSM should transition. Returning
NO_TRANSIT repeats the current state, but goes back to the scheduler
first.
(2) Wait state. This is an event processing state. No execution is
performed by a wait state. Wait states are just tables of "if event X
occurs, clear it and transition to state Y". The dispatcher returns to
the scheduler if none of the events in which the wait state has an
interest are currently pending.
(3) Out-of-band state. This is a special work state. Transitions to normal
states can be overridden when an unexpected event occurs (eg. I/O error).
Instead the dispatcher disables and clears the OOB event and transits to
the specified work state. This then acts as an ordinary work state,
though object->state points to the overridden destination. Returning
NO_TRANSIT resumes the overridden transition.
In addition, the states have names in their definitions, so there's no need for
tables of state names. Further, the EV_REQUEUE event is no longer necessary as
that is automatic for work states.
Since the states are now separate structs rather than values in an enum, it's
not possible to use comparisons other than (non-)equality between them, so use
some object->flags to indicate what phase an object is in.
The EV_RELEASE, EV_RETIRE and EV_WITHDRAW events have been squished into one
(EV_KILL). An object flag now carries the information about retirement.
Similarly, the RELEASING, RECYCLING and WITHDRAWING states have been merged
into an KILL_OBJECT state and additional states have been added for handling
waiting dependent objects (JUMPSTART_DEPS and KILL_DEPENDENTS).
A state has also been added for synchronising with parent object initialisation
(WAIT_FOR_PARENT) and another for initiating look up (PARENT_READY).
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-By: Milosz Tanski <milosz@adfin.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
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Wrap checks on object state (mostly outside of fs/fscache/object.c) with
inline functions so that the mechanism can be replaced.
Some of the state checks within object.c are left as-is as they will be
replaced.
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-By: Milosz Tanski <milosz@adfin.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
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Uninline fscache_object_init() so as not to expose some of the FS-Cache
internals to the cache backend.
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-By: Milosz Tanski <milosz@adfin.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
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Mark as cancelled an operation that is in progress rather than pending at the
time it is cancelled, and call fscache_complete_op() to cancel an operation so
that blocked ops can be started.
Signed-off-by: David Howells <dhowells@redhat.com>
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Convert the fscache_object event IDs from #defines into an enum. Also add an
extra label to the enum to carry the event count and redefine the event mask
in terms of that.
Signed-off-by: David Howells <dhowells@redhat.com>
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Provide a proper invalidation method rather than relying on the netfs retiring
the cookie it has and getting a new one. The problem with this is that isn't
easy for the netfs to make sure that it has completed/cancelled all its
outstanding storage and retrieval operations on the cookie it is retiring.
Instead, have the cache provide an invalidation method that will cancel or wait
for all currently outstanding operations before invalidating the cache, and
will cause new operations to queue up behind that. Whilst invalidation is in
progress, some requests will be rejected until the cache can stack a barrier on
the operation queue to cause new operations to be deferred behind it.
Signed-off-by: David Howells <dhowells@redhat.com>
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