Age | Commit message (Collapse) | Author | Files | Lines |
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# Conflicts:
# fs/btrfs/file.c
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For a non-existent device, old code bypasses adding it in dev's reada
queue.
And to solve problem of unfinished waitting in raid5/6,
commit 5fbc7c59fd22 ("Btrfs: fix unfinished readahead thread for
raid5/6 degraded mounting")
adding an exception for the first stripe, in short, the first
stripe will always be processed whether the device exists or not.
Actually we have a better way for the above request: just bypass
creation of the reada_extent for non-existent device, it will make
code simple and effective.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Reada background works is not designed to finish all jobs
completely, it will break in following case:
1: When a device reaches workload limit (MAX_IN_FLIGHT)
2: Total reads reach max limit (10000)
3: All devices don't have queued more jobs, often happened in DUP case
And if all background works exit with remaining jobs,
btrfs_reada_wait() will wait indefinetelly.
Above problem is rarely happened in old code, because:
1: Every work queues 2x new works
So many works reduced chances of undone jobs.
2: One work will continue 10000 times loop in case of no-jobs
It reduced no-thread window time.
But after we fixed above case, the "undone reada extents" frequently
happened.
Fix:
Check to ensure we have at least one thread if there are undone jobs
in btrfs_reada_wait().
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Reada creates 2 works for each level of tree recursively.
In case of a tree having many levels, the number of created works
is 2^level_of_tree.
Actually we don't need so many works in parallel, this patch limits
max works to BTRFS_MAX_MIRRORS * 2.
The per-fs works_counter will be also used for btrfs_reada_wait() to
check is there are background workers.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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No need to decrease dev->reada_in_flight in __readahead_hook()'s
internal and reada_extent_put().
reada_extent_put() have no chance to decrease dev->reada_in_flight
in free operation, because reada_extent have additional refcnt when
scheduled to a dev.
We can put inc and dec operation for dev->reada_in_flight to one
place instead to make logic simple and safe, and move useless
reada_extent->scheduled_for to a bool flag instead.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Remove one copy of loop to fix the typo of iterate zones.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Current code set nritems to 0 to make for_loop useless to bypass it,
and set generation's value which is not necessary.
Jump into cleanup directly is better choise.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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What __readahead_hook() need exactly is fs_info, no need to convert
fs_info to root in caller and convert back in __readahead_hook()
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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reada_start_machine_dev() already have reada_extent pointer, pass
it into __readahead_hook() directly instead of search radix_tree
will make code run faster.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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We can't release reada_extent earlier than __readahead_hook(), because
__readahead_hook() still need to use it, it is necessary to hode a refcnt
to avoid it be freed.
Actually it is not a problem after my patch named:
Avoid many times of empty loop
It make reada_extent in above line include at least one reada_extctl,
which keeps additional one refcnt for reada_extent.
But we still need this patch to make the code in pretty logic.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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level is not used in severial functions, remove them from arguments,
and remove relative code for get its value.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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When failed adding all dev_zones for a reada_extent, the extent
will have no chance to be selected to run, and keep in memory
for ever.
We should bypass this extent to avoid above case.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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If some device is not reachable, we should bypass and continus addingb
next, instead of break on bad device.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Move is_need_to_readahead contition earlier to avoid useless loop
to get relative data for readahead.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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We can see following loop(10000 times) in trace_log:
[ 75.416137] ZL_DEBUG: reada_start_machine_dev:730: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.417413] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
[ 75.418611] ZL_DEBUG: __readahead_hook:129: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.419793] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
[ 75.421016] ZL_DEBUG: reada_start_machine_dev:730: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.422324] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
[ 75.423661] ZL_DEBUG: __readahead_hook:129: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.424882] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
...(10000 times)
[ 124.101672] ZL_DEBUG: reada_start_machine_dev:730: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 124.102850] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
[ 124.104008] ZL_DEBUG: __readahead_hook:129: pid=771 comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 124.105121] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re = ffff88003741e0c0, refcnt = 2 -> 1
Reason:
If more than one user trigger reada in same extent, the first task
finished setting of reada data struct and call reada_start_machine()
to start, and the second task only add a ref_count but have not
add reada_extctl struct completely, the reada_extent can not finished
all jobs, and will be selected in __reada_start_machine() for 10000
times(total times in __reada_start_machine()).
Fix:
For a reada_extent without job, we don't need to run it, just return
0 to let caller break.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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In rechecking zone-in-tree, we still need to check zone include
our logical address.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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We can avoid additional locking-acquirment and one pair of
kref_get/put by combine two condition.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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reada_zone->end is end pos of segment:
end = start + cache->key.offset - 1;
So we need to use "<=" in condition to judge is a pos in the
segment.
The problem happened rearly, because logical pos rarely pointed
to last 4k of a blockgroup, but we need to fix it to make code
right in logic.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Introduce new mount option alias "norecovery" for nologreplay, to keep
"norecovery" behavior the same with other filesystems.
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Introduce a new mount option "nologreplay" to co-operate with "ro" mount
option to get real readonly mount, like "norecovery" in ext* and xfs.
Since the new parse_options() need to check new flags at remount time,
so add a new parameter for parse_options().
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Tested-by: Austin S. Hemmelgarn <ahferroin7@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Current "recovery" mount option will only try to use backup root.
However the word "recovery" is too generic and may be confusing for some
users.
Here introduce a new and more specific mount option, "usebackuproot" to
replace "recovery" mount option.
"Recovery" will be kept for compatibility reason, but will be
deprecated.
Also, since "usebackuproot" will only affect mount behavior and after
open_ctree() it has nothing to do with the filesystem, so clear the flag
after mount succeeded.
This provides the basis for later unified "norecovery" mount option.
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
[ dropped usebackuproot from show_mount, added note about 'recovery' to
docs ]
Signed-off-by: David Sterba <dsterba@suse.com>
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Signed-off-by: David Sterba <dsterba@suse.com>
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Signed-off-by: David Sterba <dsterba@suse.com>
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Signed-off-by: David Sterba <dsterba@suse.com>
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The number of distinct key types is not that big that we could waste one
for something new we want to store in the tree.
Similar to the temporary items, we'll introduce a new name for an
existing key value and use the objectid for further extension. The
victim is the BTRFS_DEV_STATS_KEY (248).
The device stats are an example of a permanent item.
Signed-off-by: David Sterba <dsterba@suse.com>
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No visible change.
Signed-off-by: David Sterba <dsterba@suse.com>
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The number of distinct key types is not that big that we could waste one
for something new we want to store in the tree. We'll introduce a new
name for an existing key value and use the objectid for further
extension. The victim is the BTRFS_BALANCE_ITEM_KEY (248).
The nature of the balance status item is a good example of the temporary
item. It exists from beginning of the balance, keeps the status until it
finishes.
Signed-off-by: David Sterba <dsterba@suse.com>
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Kcalloc is functionally equivalent and does overflow checks.
Signed-off-by: David Sterba <dsterba@suse.com>
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We can safely use GFP_KERNEL in the functions called from the ioctl
handlers. Here we can allocate up to 32k so less pressure to the
allocator could help.
Signed-off-by: David Sterba <dsterba@suse.com>
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We can safely use GFP_KERNEL in the functions called from the ioctl
handlers.
Signed-off-by: David Sterba <dsterba@suse.com>
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Readdir is initiated from userspace and is not on the critical
writeback path, we don't need to use GFP_NOFS for allocations.
Signed-off-by: David Sterba <dsterba@suse.com>
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Fallocate is initiated from userspace and is not on the critical
writeback path, we don't need to use GFP_NOFS for allocations.
Signed-off-by: David Sterba <dsterba@suse.com>
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We don't need to use GFP_NOFS in all contexts, eg. during mount or for
dummy root tree, but we might for the the log tree creation.
Signed-off-by: David Sterba <dsterba@suse.com>
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Scrub is not on the critical writeback path we don't need to use
GFP_NOFS for all allocations. The failures are handled and stats passed
back to userspace.
Let's use GFP_KERNEL on the paths where everything is ok, ie. setup the
global structures and the IO submission paths.
Functions that do the repair and fixups still use GFP_NOFS as we might
want to skip any other filesystem activity if we encounter an error.
This could turn out to be unnecessary, but requires more review compared
to the easy cases in this patch.
Signed-off-by: David Sterba <dsterba@suse.com>
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The readahead framework is not on the critical writeback path we don't
need to use GFP_NOFS for allocations. All error paths are handled and
the readahead failures are not fatal. The actual users (scrub,
dev-replace) will trigger reads if the blocks are not found in cache.
Signed-off-by: David Sterba <dsterba@suse.com>
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The send operation is not on the critical writeback path we don't need
to use GFP_NOFS for allocations. All error paths are handled and the
whole operation is restartable.
Signed-off-by: David Sterba <dsterba@suse.com>
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git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc
Pull ARM SoC fixes from Olof Johansson:
"The first real batch of fixes for this release cycle, so there are a
few more than usual.
Most of these are fixes and tweaks to board support (DT bugfixes,
etc). I've also picked up a couple of small cleanups that seemed
innocent enough that there was little reason to wait (const/
__initconst and Kconfig deps).
Quite a bit of the changes on OMAP were due to fixes to no longer
write to rodata from assembly when ARM_KERNMEM_PERMS was enabled, but
there were also other fixes.
Kirkwood had a bunch of gpio fixes for some boards. OMAP had RTC
fixes on OMAP5, and Nomadik had changes to MMC parameters in DT.
All in all, mostly the usual mix of various fixes"
* tag 'armsoc-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc: (46 commits)
ARM: multi_v7_defconfig: enable DW_WATCHDOG
ARM: nomadik: fix up SD/MMC DT settings
ARM64: tegra: Add chosen node for tegra132 norrin
ARM: realview: use "depends on" instead of "if" after prompt
ARM: tango: use "depends on" instead of "if" after prompt
ARM: tango: use const and __initconst for smp_operations
ARM: realview: use const and __initconst for smp_operations
bus: uniphier-system-bus: revive tristate prompt
arm64: dts: Add missing DMA Abort interrupt to Juno
bus: vexpress-config: Add missing of_node_put
ARM: dts: am57xx: sbc-am57x: correct Eth PHY settings
ARM: dts: am57xx: cl-som-am57x: fix CPSW EMAC pinmux
ARM: dts: am57xx: sbc-am57x: fix UART3 pinmux
ARM: dts: am57xx: cl-som-am57x: update SPI Flash frequency
ARM: dts: am57xx: cl-som-am57x: set HOST mode for USB2
ARM: dts: am57xx: sbc-am57x: fix SB-SOM EEPROM I2C address
ARM: dts: LogicPD Torpedo: Revert Duplicative Entries
ARM: dts: am437x: pixcir_tangoc: use correct flags for irq types
ARM: dts: am4372: fix irq type for arm twd and global timer
ARM: dts: at91: sama5d4 xplained: fix phy0 IRQ type
...
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git://git.linaro.org/landing-teams/working/fujitsu/integration
Pull mailbox fixes from Jassi Brar:
- fix getting element from the pcc-channels array by simply indexing
into it
- prevent building mailbox-test driver for archs that don't have IOMEM
* 'mailbox-devel' of git://git.linaro.org/landing-teams/working/fujitsu/integration:
mailbox: Fix dependencies for !HAS_IOMEM archs
mailbox: pcc: fix channel calculation in get_pcc_channel()
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git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb
Pull USB fixes from Greg KH:
"Here are some USB fixes for 4.5-rc3.
The usual, xhci fixes for reported issues, combined with some small
gadget driver fixes, and a MAINTAINERS file update. All have been in
linux-next with no reported issues"
* tag 'usb-4.5-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb:
xhci: harden xhci_find_next_ext_cap against device removal
xhci: Fix list corruption in urb dequeue at host removal
usb: host: xhci-plat: fix NULL pointer in probe for device tree case
usb: xhci-mtk: fix AHB bus hang up caused by roothubs polling
usb: xhci-mtk: fix bpkts value of LS/HS periodic eps not behind TT
usb: xhci: apply XHCI_PME_STUCK_QUIRK to Intel Broxton-M platforms
usb: xhci: set SSIC port unused only if xhci_suspend succeeds
usb: xhci: add a quirk bit for ssic port unused
usb: xhci: handle both SSIC ports in PME stuck quirk
usb: dwc3: gadget: set the OTG flag in dwc3 gadget driver.
Revert "xhci: don't finish a TD if we get a short-transfer event mid TD"
MAINTAINERS: fix my email address
usb: dwc2: Fix probe problem on bcm2835
Revert "usb: dwc2: Move reset into dwc2_get_hwparams()"
usb: musb: ux500: Fix NULL pointer dereference at system PM
usb: phy: mxs: declare variable with initialized value
usb: phy: msm: fix error handling in probe.
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git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging
Pull staging and IIO driver fixes from Greg KH:
"Here are some IIO and staging driver fixes for 4.5-rc3.
All of them, except one, are for IIO drivers, and one is for a speakup
driver fix caused by some earlier patches, to resolve a reported build
failure"
* tag 'staging-4.5-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging:
Staging: speakup: Fix allyesconfig build on mn10300
iio: dht11: Use boottime
iio: ade7753: avoid uninitialized data
iio: pressure: mpl115: fix temperature offset sign
iio: imu: Fix dependencies for !HAS_IOMEM archs
staging: iio: Fix dependencies for !HAS_IOMEM archs
iio: adc: Fix dependencies for !HAS_IOMEM archs
iio: inkern: fix a NULL dereference on error
iio:adc:ti_am335x_adc Fix buffered mode by identifying as software buffer.
iio: light: acpi-als: Report data as processed
iio: dac: mcp4725: set iio name property in sysfs
iio: add HAS_IOMEM dependency to VF610_ADC
iio: add IIO_TRIGGER dependency to STK8BA50
iio: proximity: lidar: correct return value
iio-light: Use a signed return type for ltr501_match_samp_freq()
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Merge fixes from Andrew Morton:
"22 fixes"
* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (22 commits)
epoll: restrict EPOLLEXCLUSIVE to POLLIN and POLLOUT
radix-tree: fix oops after radix_tree_iter_retry
MAINTAINERS: trim the file triggers for ABI/API
dax: dirty inode only if required
thp: make deferred_split_scan() work again
mm: replace vma_lock_anon_vma with anon_vma_lock_read/write
ocfs2/dlm: clear refmap bit of recovery lock while doing local recovery cleanup
um: asm/page.h: remove the pte_high member from struct pte_t
mm, hugetlb: don't require CMA for runtime gigantic pages
mm/hugetlb: fix gigantic page initialization/allocation
mm: downgrade VM_BUG in isolate_lru_page() to warning
mempolicy: do not try to queue pages from !vma_migratable()
mm, vmstat: fix wrong WQ sleep when memory reclaim doesn't make any progress
vmstat: make vmstat_update deferrable
mm, vmstat: make quiet_vmstat lighter
mm/Kconfig: correct description of DEFERRED_STRUCT_PAGE_INIT
memblock: don't mark memblock_phys_mem_size() as __init
dump_stack: avoid potential deadlocks
mm: validate_mm browse_rb SMP race condition
m32r: fix build failure due to SMP and MMU
...
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git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client
Pull Ceph fixes from Sage Weil:
"We have a few wire protocol compatibility fixes, ports of a few recent
CRUSH mapping changes, and a couple error path fixes"
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client:
libceph: MOSDOpReply v7 encoding
libceph: advertise support for TUNABLES5
crush: decode and initialize chooseleaf_stable
crush: add chooseleaf_stable tunable
crush: ensure take bucket value is valid
crush: ensure bucket id is valid before indexing buckets array
ceph: fix snap context leak in error path
ceph: checking for IS_ERR instead of NULL
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Pull drm fixes from Dave Airlie:
"Fixes all over the place:
- amdkfd: two static checker fixes
- mst: a bunch of static checker and spec/hw interaction fixes
- amdgpu: fix Iceland hw properly, and some fiji bugs, along with
some write-combining fixes.
- exynos: some regression fixes
- adv7511: fix some EDID reading issues"
* 'drm-fixes' of git://people.freedesktop.org/~airlied/linux: (38 commits)
drm/dp/mst: deallocate payload on port destruction
drm/dp/mst: Reverse order of MST enable and clearing VC payload table.
drm/dp/mst: move GUID storage from mgr, port to only mst branch
drm/dp/mst: change MST detection scheme
drm/dp/mst: Calculate MST PBN with 31.32 fixed point
drm: Add drm_fixp_from_fraction and drm_fixp2int_ceil
drm/mst: Add range check for max_payloads during init
drm/mst: Don't ignore the MST PBN self-test result
drm: fix missing reference counting decrease
drm/amdgpu: disable uvd and vce clockgating on Fiji
drm/amdgpu: remove exp hardware support from iceland
drm/amdgpu: load MEC ucode manually on iceland
drm/amdgpu: don't load MEC2 on topaz
drm/amdgpu: drop topaz support from gmc8 module
drm/amdgpu: pull topaz gmc bits into gmc_v7
drm/amdgpu: The VI specific EXE bit should only apply to GMC v8.0 above
drm/amdgpu: iceland use CI based MC IP
drm/amdgpu: move gmc7 support out of CIK dependency
drm/amdgpu/gfx7: enable cp inst/reg error interrupts
drm/amdgpu/gfx8: enable cp inst/reg error interrupts
...
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git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
Pull power management and ACPI fixes from Rafael Wysocki:
"These are: a fix for a recently introduced false-positive warnings
about PM domain pointers being changed inappropriately (harmless but
annoying), an MCH size workaround quirk for one more platform, a
compiler warning fix (generic power domains framework), an ACPI LPSS
(Intel SoCs) driver fixup and a cleanup of the ACPI CPPC core code.
Specifics:
- PM core fix to avoid false-positive warnings generated when the
pm_domain field is cleared for a device that appears to be bound to
a driver (Rafael Wysocki).
- New MCH size workaround quirk for Intel Haswell-ULT (Josh Boyer).
- Fix for an "unused function" compiler warning in the generic power
domains framework (Ulf Hansson).
- Fixup for the ACPI driver for Intel SoCs (acpi-lpss) to set the PM
domain pointer of a device properly in one place that was
overlooked by a recent PM core update (Andy Shevchenko).
- Removal of a redundant function declaration in the ACPI CPPC core
code (Timur Tabi)"
* tag 'pm+acpi-4.5-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
PM: Avoid false-positive warnings in dev_pm_domain_set()
PM / Domains: Silence compiler warning for an unused function
ACPI / CPPC: remove redundant mbox_send_message() declaration
ACPI / LPSS: set PM domain via helper setter
PNP: Add Haswell-ULT to Intel MCH size workaround
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In the current implementation of the EPOLLEXCLUSIVE flag (added for
4.5-rc1), if epoll waiters create different POLL* sets and register them
as exclusive against the same target fd, the current implementation will
stop waking any further waiters once it finds the first idle waiter.
This means that waiters could miss wakeups in certain cases.
For example, when we wake up a pipe for reading we do:
wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLRDNORM); So if
one epoll set or epfd is added to pipe p with POLLIN and a second set
epfd2 is added to pipe p with POLLRDNORM, only epfd may receive the
wakeup since the current implementation will stop after it finds any
intersection of events with a waiter that is blocked in epoll_wait().
We could potentially address this by requiring all epoll waiters that
are added to p be required to pass the same set of POLL* events. IE the
first EPOLL_CTL_ADD that passes EPOLLEXCLUSIVE establishes the set POLL*
flags to be used by any other epfds that are added as EPOLLEXCLUSIVE.
However, I think it might be somewhat confusing interface as we would
have to reference count the number of users for that set, and so
userspace would have to keep track of that count, or we would need a
more involved interface. It also adds some shared state that we'd have
store somewhere. I don't think anybody will want to bloat
__wait_queue_head for this.
I think what we could do instead, is to simply restrict EPOLLEXCLUSIVE
such that it can only be specified with EPOLLIN and/or EPOLLOUT. So
that way if the wakeup includes 'POLLIN' and not 'POLLOUT', we can stop
once we hit the first idle waiter that specifies the EPOLLIN bit, since
any remaining waiters that only have 'POLLOUT' set wouldn't need to be
woken. Likewise, we can do the same thing if 'POLLOUT' is in the wakeup
bit set and not 'POLLIN'. If both 'POLLOUT' and 'POLLIN' are set in the
wake bit set (there is at least one example of this I saw in fs/pipe.c),
then we just wake the entire exclusive list. Having both 'POLLOUT' and
'POLLIN' both set should not be on any performance critical path, so I
think that's ok (in fs/pipe.c its in pipe_release()). We also continue
to include EPOLLERR and EPOLLHUP by default in any exclusive set. Thus,
the user can specify EPOLLERR and/or EPOLLHUP but is not required to do
so.
Since epoll waiters may be interested in other events as well besides
EPOLLIN, EPOLLOUT, EPOLLERR and EPOLLHUP, these can still be added by
doing a 'dup' call on the target fd and adding that as one normally
would with EPOLL_CTL_ADD. Since I think that the POLLIN and POLLOUT
events are what we are interest in balancing, I think that the 'dup'
thing could perhaps be added to only one of the waiter threads.
However, I think that EPOLLIN, EPOLLOUT, EPOLLERR and EPOLLHUP should be
sufficient for the majority of use-cases.
Since EPOLLEXCLUSIVE is intended to be used with a target fd shared
among multiple epfds, where between 1 and n of the epfds may receive an
event, it does not satisfy the semantics of EPOLLONESHOT where only 1
epfd would get an event. Thus, it is not allowed to be specified in
conjunction with EPOLLEXCLUSIVE.
EPOLL_CTL_MOD is also not allowed if the fd was previously added as
EPOLLEXCLUSIVE. It seems with the limited number of flags to not be as
interesting, but this could be relaxed at some further point.
Signed-off-by: Jason Baron <jbaron@akamai.com>
Tested-by: Madars Vitolins <m@silodev.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Eric Wong <normalperson@yhbt.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Hagen Paul Pfeifer <hagen@jauu.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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