Jan Kara 11c7aa0dde rq-qos: fix missed wake-ups in rq_qos_throttle try two ... Commit 545fbd0775 ("rq-qos: fix missed wake-ups in rq_qos_throttle") tried to fix a problem that a process could be sleeping in rq_qos_wait() without anyone to wake it up. However the fix is not complete and the following can still happen: CPU1 (waiter1) CPU2 (waiter2) CPU3 (waker) rq_qos_wait() rq_qos_wait() acquire_inflight_cb() -> fails acquire_inflight_cb() -> fails completes IOs, inflight decreased prepare_to_wait_exclusive() prepare_to_wait_exclusive() has_sleeper = !wq_has_single_sleeper() -> true as there are two sleepers has_sleeper = !wq_has_single_sleeper() -> true io_schedule() io_schedule() Deadlock as now there's nobody to wakeup the two waiters. The logic automatically blocking when there are already sleepers is really subtle and the only way to make it work reliably is that we check whether there are some waiters in the queue when adding ourselves there. That way, we are guaranteed that at least the first process to enter the wait queue will recheck the waiting condition before going to sleep and thus guarantee forward progress. Fixes: 545fbd0775 ("rq-qos: fix missed wake-ups in rq_qos_throttle") CC: stable@vger.kernel.org Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20210607112613.25344-1-jack@suse.cz Signed-off-by: Jens Axboe <axboe@kernel.dk>		2021-06-08 15:12:57 -06:00
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acpi
asm-generic	mm: remove xlate_dev_kmem_ptr()	2021-05-07 00:26:34 -07:00
clocksource
crypto
drm
dt-bindings	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input	2021-05-06 23:37:55 -07:00
keys	integrity-v5.13	2021-05-01 15:32:18 -07:00
kunit
kvm
linux	rq-qos: fix missed wake-ups in rq_qos_throttle try two	2021-06-08 15:12:57 -06:00
math-emu
media
memory
misc
net	mm: fix struct page layout on 32-bit systems	2021-05-14 19:41:32 -07:00
pcmcia
ras
rdma
scsi
soc
sound
target
trace	NFS client updates for Linux 5.13	2021-05-07 11:23:41 -07:00
uapi	Merge branch 'for-v5.13-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace	2021-05-21 06:12:52 -10:00
vdso
video
xen	xen/arm: move xen_swiotlb_detect to arm/swiotlb-xen.h	2021-05-14 15:52:05 +02:00