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| author | Jan Kara <jack@suse.cz> | 2021-06-07 14:26:13 +0300 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2021-06-09 00:12:57 +0300 |
| commit | 11c7aa0ddea8611007768d3e6b58d45dc60a19e1 (patch) | |
| tree | ee3ebd955e2765aa172b9647f23bea6f1db4a742 /block | |
| parent | c9c9762d4d44dcb1b2ba90cfb4122dc11ceebf31 (diff) | |
| download | linux-11c7aa0ddea8611007768d3e6b58d45dc60a19e1.tar.xz | |
rq-qos: fix missed wake-ups in rq_qos_throttle try two
Commit 545fbd0775ba ("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: 545fbd0775ba ("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>
Diffstat (limited to 'block')
| -rw-r--r-- | block/blk-rq-qos.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c index 656460636ad3..e83af7bc7591 100644 --- a/block/blk-rq-qos.c +++ b/block/blk-rq-qos.c @@ -266,8 +266,8 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data, if (!has_sleeper && acquire_inflight_cb(rqw, private_data)) return; - prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE); - has_sleeper = !wq_has_single_sleeper(&rqw->wait); + has_sleeper = !prepare_to_wait_exclusive(&rqw->wait, &data.wq, + TASK_UNINTERRUPTIBLE); do { /* The memory barrier in set_task_state saves us here. */ if (data.got_token) |