kernel/linux.git/drivers/md/bcache/writeback.h, branch linux-5.11.y

bcache: fix overflow in offset_to_stripe()

2020-07-25T13:38:20+00:00

offset_to_stripe() returns the stripe number (in type unsigned int) from an offset (in type uint64_t) by the following calculation, do_div(offset, d->stripe_size); For large capacity backing device (e.g. 18TB) with small stripe size (e.g. 4KB), the result is 4831838208 and exceeds UINT_MAX. The actual returned value which caller receives is 536870912, due to the overflow. Indeed in bcache_device_init(), bcache_device->nr_stripes is limited in range [1, INT_MAX]. Therefore all valid stripe numbers in bcache are in range [0, bcache_dev->nr_stripes - 1]. This patch adds a upper limition check in offset_to_stripe(): the max valid stripe number should be less than bcache_device->nr_stripes. If the calculated stripe number from do_div() is equal to or larger than bcache_device->nr_stripe, -EINVAL will be returned. (Normally nr_stripes is less than INT_MAX, exceeding upper limitation doesn't mean overflow, therefore -EOVERFLOW is not used as error code.) This patch also changes nr_stripes' type of struct bcache_device from 'unsigned int' to 'int', and return value type of offset_to_stripe() from 'unsigned int' to 'int', to match their exact data ranges. All locations where bcache_device->nr_stripes and offset_to_stripe() are referenced also get updated for the above type change. Reported-and-tested-by: Ken Raeburn Signed-off-by: Coly Li Cc: stable@vger.kernel.org Link: https://bugzilla.redhat.com/show_bug.cgi?id=1783075 Signed-off-by: Jens Axboe

bcache: make bch_sectors_dirty_init() to be multithreaded

2020-03-22T16:06:57+00:00

When attaching a cached device (a.k.a backing device) to a cache device, bch_sectors_dirty_init() is called to count dirty sectors and stripes (see what bcache_dev_sectors_dirty_add() does) on the cache device. The counting is done by a single thread recursive function bch_btree_map_keys() to iterate all the bcache btree nodes. If the btree has huge number of nodes, bch_sectors_dirty_init() will take quite long time. In my testing, if the registering cache set has a existed UUID which matches a already registered cached device, the automatical attachment during the registration may take more than 55 minutes. This is too long for waiting the bcache to work in real deployment. Fortunately when bch_sectors_dirty_init() is called, no other thread will access the btree yet, it is safe to do a read-only parallelized dirty sectors counting by multiple threads. This patch tries to create multiple threads, and each thread tries to one-by-one count dirty sectors from the sub-tree indexed by a root node key which the thread fetched. After the sub-tree is counted, the counting thread will continue to fetch another root node key, until the fetched key is NULL. How many threads in parallel depends on the number of keys from the btree root node, and the number of online CPU core. The thread number will be the less number but no more than BCH_DIRTY_INIT_THRD_MAX. If there are only 2 keys in root node, it can only be 2x times faster by this patch. But if there are 10 keys in the root node, with this patch it can be 10x times faster. Signed-off-by: Coly Li Cc: Christoph Hellwig Signed-off-by: Jens Axboe

bcache: never writeback a discard operation

2019-02-09T14:18:31+00:00

Some users see panics like the following when performing fstrim on a bcached volume: [ 529.803060] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 [ 530.183928] #PF error: [normal kernel read fault] [ 530.412392] PGD 8000001f42163067 P4D 8000001f42163067 PUD 1f42168067 PMD 0 [ 530.750887] Oops: 0000 [#1] SMP PTI [ 530.920869] CPU: 10 PID: 4167 Comm: fstrim Kdump: loaded Not tainted 5.0.0-rc1+ #3 [ 531.290204] Hardware name: HP ProLiant DL360 Gen9/ProLiant DL360 Gen9, BIOS P89 12/27/2015 [ 531.693137] RIP: 0010:blk_queue_split+0x148/0x620 [ 531.922205] Code: 60 38 89 55 a0 45 31 db 45 31 f6 45 31 c9 31 ff 89 4d 98 85 db 0f 84 7f 04 00 00 44 8b 6d 98 4c 89 ee 48 c1 e6 04 49 03 70 78 <8b> 46 08 44 8b 56 0c 48 8b 16 44 29 e0 39 d8 48 89 55 a8 0f 47 c3 [ 532.838634] RSP: 0018:ffffb9b708df39b0 EFLAGS: 00010246 [ 533.093571] RAX: 00000000ffffffff RBX: 0000000000046000 RCX: 0000000000000000 [ 533.441865] RDX: 0000000000000200 RSI: 0000000000000000 RDI: 0000000000000000 [ 533.789922] RBP: ffffb9b708df3a48 R08: ffff940d3b3fdd20 R09: 0000000000000000 [ 534.137512] R10: ffffb9b708df3958 R11: 0000000000000000 R12: 0000000000000000 [ 534.485329] R13: 0000000000000000 R14: 0000000000000000 R15: ffff940d39212020 [ 534.833319] FS: 00007efec26e3840(0000) GS:ffff940d1f480000(0000) knlGS:0000000000000000 [ 535.224098] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 535.504318] CR2: 0000000000000008 CR3: 0000001f4e256004 CR4: 00000000001606e0 [ 535.851759] Call Trace: [ 535.970308] ? mempool_alloc_slab+0x15/0x20 [ 536.174152] ? bch_data_insert+0x42/0xd0 [bcache] [ 536.403399] blk_mq_make_request+0x97/0x4f0 [ 536.607036] generic_make_request+0x1e2/0x410 [ 536.819164] submit_bio+0x73/0x150 [ 536.980168] ? submit_bio+0x73/0x150 [ 537.149731] ? bio_associate_blkg_from_css+0x3b/0x60 [ 537.391595] ? _cond_resched+0x1a/0x50 [ 537.573774] submit_bio_wait+0x59/0x90 [ 537.756105] blkdev_issue_discard+0x80/0xd0 [ 537.959590] ext4_trim_fs+0x4a9/0x9e0 [ 538.137636] ? ext4_trim_fs+0x4a9/0x9e0 [ 538.324087] ext4_ioctl+0xea4/0x1530 [ 538.497712] ? _copy_to_user+0x2a/0x40 [ 538.679632] do_vfs_ioctl+0xa6/0x600 [ 538.853127] ? __do_sys_newfstat+0x44/0x70 [ 539.051951] ksys_ioctl+0x6d/0x80 [ 539.212785] __x64_sys_ioctl+0x1a/0x20 [ 539.394918] do_syscall_64+0x5a/0x110 [ 539.568674] entry_SYSCALL_64_after_hwframe+0x44/0xa9 We have observed it where both: 1) LVM/devmapper is involved (bcache backing device is LVM volume) and 2) writeback cache is involved (bcache cache_mode is writeback) On one machine, we can reliably reproduce it with: # echo writeback > /sys/block/bcache0/bcache/cache_mode (not sure whether above line is required) # mount /dev/bcache0 /test # for i in {0..10}; do file="$(mktemp /test/zero.XXX)" dd if=/dev/zero of="$file" bs=1M count=256 sync rm $file done # fstrim -v /test Observing this with tracepoints on, we see the following writes: fstrim-18019 [022] .... 91107.302026: bcache_write: 73f95583-561c-408f-a93a-4cbd2498f5c8 inode 0 DS 4260112 + 196352 hit 0 bypass 1 fstrim-18019 [022] .... 91107.302050: bcache_write: 73f95583-561c-408f-a93a-4cbd2498f5c8 inode 0 DS 4456464 + 262144 hit 0 bypass 1 fstrim-18019 [022] .... 91107.302075: bcache_write: 73f95583-561c-408f-a93a-4cbd2498f5c8 inode 0 DS 4718608 + 81920 hit 0 bypass 1 fstrim-18019 [022] .... 91107.302094: bcache_write: 73f95583-561c-408f-a93a-4cbd2498f5c8 inode 0 DS 5324816 + 180224 hit 0 bypass 1 fstrim-18019 [022] .... 91107.302121: bcache_write: 73f95583-561c-408f-a93a-4cbd2498f5c8 inode 0 DS 5505040 + 262144 hit 0 bypass 1 fstrim-18019 [022] .... 91107.302145: bcache_write: 73f95583-561c-408f-a93a-4cbd2498f5c8 inode 0 DS 5767184 + 81920 hit 0 bypass 1 fstrim-18019 [022] .... 91107.308777: bcache_write: 73f95583-561c-408f-a93a-4cbd2498f5c8 inode 0 DS 6373392 + 180224 hit 1 bypass 0 Note the final one has different hit/bypass flags. This is because in should_writeback(), we were hitting a case where the partial stripe condition was returning true and so should_writeback() was returning true early. If that hadn't been the case, it would have hit the would_skip test, and as would_skip == s->iop.bypass == true, should_writeback() would have returned false. Looking at the git history from 'commit 72c270612bd3 ("bcache: Write out full stripes")', it looks like the idea was to optimise for raid5/6: * If a stripe is already dirty, force writes to that stripe to writeback mode - to help build up full stripes of dirty data To fix this issue, make sure that should_writeback() on a discard op never returns true. More details of debugging: https://www.spinics.net/lists/linux-bcache/msg06996.html Previous reports: - https://bugzilla.kernel.org/show_bug.cgi?id=201051 - https://bugzilla.kernel.org/show_bug.cgi?id=196103 - https://www.spinics.net/lists/linux-bcache/msg06885.html (Coly Li: minor modification to follow maximum 75 chars per line rule) Cc: Kent Overstreet Cc: stable@vger.kernel.org Fixes: 72c270612bd3 ("bcache: Write out full stripes") Signed-off-by: Daniel Axtens Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: make cutoff_writeback and cutoff_writeback_sync tunable

2018-12-13T15:15:54+00:00

Currently the cutoff writeback and cutoff writeback sync thresholds are defined by CUTOFF_WRITEBACK (40) and CUTOFF_WRITEBACK_SYNC (70) as static values. Most of time these they work fine, but when people want to do research on bcache writeback mode performance tuning, there is no chance to modify the soft and hard cutoff writeback values. This patch introduces two module parameters bch_cutoff_writeback_sync and bch_cutoff_writeback which permit people to tune the values when loading bcache.ko. If they are not specified by module loading, current values CUTOFF_WRITEBACK_SYNC and CUTOFF_WRITEBACK will be used as default and nothing changes. When people want to tune this two values, - cutoff_writeback can be set in range [1, 70] - cutoff_writeback_sync can be set in range [1, 90] - cutoff_writeback always <= cutoff_writeback_sync The default values are strongly recommended to most of users for most of workloads. Anyway, if people wants to take their own risk to do research on new writeback cutoff tuning for their own workload, now they can make it. Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: option to automatically run gc thread after writeback

2018-12-13T15:15:54+00:00

The option gc_after_writeback is disabled by default, because garbage collection will discard SSD data which drops cached data. Echo 1 into /sys/fs/bcache//internal/gc_after_writeback will enable this option, which wakes up gc thread when writeback accomplished and all cached data is clean. This option is helpful for people who cares writing performance more. In heavy writing workload, all cached data can be clean only happens when writeback thread cleans all cached data in I/O idle time. In such situation a following gc running may help to shrink bcache B+ tree and discard more clean data, which may be helpful for future writing requests. If you are not sure whether this is helpful for your own workload, please leave it as disabled by default. Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: add identifier names to arguments of function definitions

2018-08-11T21:46:41+00:00

There are many function definitions do not have identifier argument names, scripts/checkpatch.pl complains warnings like this, WARNING: function definition argument 'struct bcache_device *' should also have an identifier name #16735: FILE: writeback.h:120: +void bch_sectors_dirty_init(struct bcache_device *); This patch adds identifier argument names to all bcache function definitions to fix such warnings. Signed-off-by: Coly Li Reviewed: Shenghui Wang Signed-off-by: Jens Axboe

bcache: style fix to replace 'unsigned' by 'unsigned int'

2018-08-11T21:46:41+00:00

This patch fixes warning reported by checkpatch.pl by replacing 'unsigned' with 'unsigned int'. Signed-off-by: Coly Li Reviewed-by: Shenghui Wang Signed-off-by: Jens Axboe

bcache: simplify the calculation of the total amount of flash dirty data

2018-07-27T15:15:46+00:00

Currently we calculate the total amount of flash only devices dirty data by adding the dirty data of each flash only device under registering locker. It is very inefficient. In this patch, we add a member flash_dev_dirty_sectors in struct cache_set to record the total amount of flash only devices dirty data in real time, so we didn't need to calculate the total amount of dirty data any more. Signed-off-by: Tang Junhui Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: Fix indentation

2018-03-19T02:15:20+00:00

This patch avoids that smatch complains about inconsistent indentation. Signed-off-by: Bart Van Assche Reviewed-by: Michael Lyle Reviewed-by: Coly Li Signed-off-by: Jens Axboe

bcache: fix cached_dev->count usage for bch_cache_set_error()

2018-03-19T02:15:20+00:00

When bcache metadata I/O fails, bcache will call bch_cache_set_error() to retire the whole cache set. The expected behavior to retire a cache set is to unregister the cache set, and unregister all backing device attached to this cache set, then remove sysfs entries of the cache set and all attached backing devices, finally release memory of structs cache_set, cache, cached_dev and bcache_device. In my testing when journal I/O failure triggered by disconnected cache device, sometimes the cache set cannot be retired, and its sysfs entry /sys/fs/bcache/ still exits and the backing device also references it. This is not expected behavior. When metadata I/O failes, the call senquence to retire whole cache set is, bch_cache_set_error() bch_cache_set_unregister() bch_cache_set_stop() __cache_set_unregister() <- called as callback by calling clousre_queue(&c->caching) cache_set_flush() <- called as a callback when refcount of cache_set->caching is 0 cache_set_free() <- called as a callback when refcount of catch_set->cl is 0 bch_cache_set_release() <- called as a callback when refcount of catch_set->kobj is 0 I find if kernel thread bch_writeback_thread() quits while-loop when kthread_should_stop() is true and searched_full_index is false, clousre callback cache_set_flush() set by continue_at() will never be called. The result is, bcache fails to retire whole cache set. cache_set_flush() will be called when refcount of closure c->caching is 0, and in function bcache_device_detach() refcount of closure c->caching is released to 0 by clousre_put(). In metadata error code path, function bcache_device_detach() is called by cached_dev_detach_finish(). This is a callback routine being called when cached_dev->count is 0. This refcount is decreased by cached_dev_put(). The above dependence indicates, cache_set_flush() will be called when refcount of cache_set->cl is 0, and refcount of cache_set->cl to be 0 when refcount of cache_dev->count is 0. The reason why sometimes cache_dev->count is not 0 (when metadata I/O fails and bch_cache_set_error() called) is, in bch_writeback_thread(), refcount of cache_dev is not decreased properly. In bch_writeback_thread(), cached_dev_put() is called only when searched_full_index is true and cached_dev->writeback_keys is empty, a.k.a there is no dirty data on cache. In most of run time it is correct, but when bch_writeback_thread() quits the while-loop while cache is still dirty, current code forget to call cached_dev_put() before this kernel thread exits. This is why sometimes cache_set_flush() is not executed and cache set fails to be retired. The reason to call cached_dev_put() in bch_writeback_rate() is, when the cache device changes from clean to dirty, cached_dev_get() is called, to make sure during writeback operatiions both backing and cache devices won't be released. Adding following code in bch_writeback_thread() does not work, static int bch_writeback_thread(void *arg) } + if (atomic_read(&dc->has_dirty)) + cached_dev_put() + return 0; } because writeback kernel thread can be waken up and start via sysfs entry: echo 1 > /sys/block/bcache/bcache/writeback_running It is difficult to check whether backing device is dirty without race and extra lock. So the above modification will introduce potential refcount underflow in some conditions. The correct fix is, to take cached dev refcount when creating the kernel thread, and put it before the kernel thread exits. Then bcache does not need to take a cached dev refcount when cache turns from clean to dirty, or to put a cached dev refcount when cache turns from ditry to clean. The writeback kernel thread is alwasy safe to reference data structure from cache set, cache and cached device (because a refcount of cache device is taken for it already), and no matter the kernel thread is stopped by I/O errors or system reboot, cached_dev->count can always be used correctly. The patch is simple, but understanding how it works is quite complicated. Changelog: v2: set dc->writeback_thread to NULL in this patch, as suggested by Hannes. v1: initial version for review. Signed-off-by: Coly Li Reviewed-by: Hannes Reinecke Reviewed-by: Michael Lyle Cc: Michael Lyle Cc: Junhui Tang Signed-off-by: Jens Axboe