This is a note to let you know that I've just added the patch titled
io-wq: serialize hash clear with wakeup
to the 5.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
io-wq-serialize-hash-clear-with-wakeup.patch
and it can be found in the queue-5.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Mon Nov 15 03:27:04 PM CET 2021
From: Jens Axboe <axboe@xxxxxxxxx>
Date: Sun, 14 Nov 2021 07:36:47 -0700
Subject: io-wq: serialize hash clear with wakeup
From: Jens Axboe <axboe@xxxxxxxxx>
commit d3e3c102d107bb84251455a298cf475f24bab995 upstream.
We need to ensure that we serialize the stalled and hash bits with the
wait_queue wait handler, or we could be racing with someone modifying
the hashed state after we find it busy, but before we then give up and
wait for it to be cleared. This can cause random delays or stalls when
handling buffered writes for many files, where some of these files cause
hash collisions between the worker threads.
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Daniel Black <daniel@xxxxxxxxxxx>
Fixes: e941894eae31 ("io-wq: make buffered file write hashed work map per-ctx")
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/io-wq.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -401,9 +401,10 @@ static inline unsigned int io_get_work_h
return work->flags >> IO_WQ_HASH_SHIFT;
}
-static void io_wait_on_hash(struct io_wqe *wqe, unsigned int hash)
+static bool io_wait_on_hash(struct io_wqe *wqe, unsigned int hash)
{
struct io_wq *wq = wqe->wq;
+ bool ret = false;
spin_lock_irq(&wq->hash->wait.lock);
if (list_empty(&wqe->wait.entry)) {
@@ -411,9 +412,11 @@ static void io_wait_on_hash(struct io_wq
if (!test_bit(hash, &wq->hash->map)) {
__set_current_state(TASK_RUNNING);
list_del_init(&wqe->wait.entry);
+ ret = true;
}
}
spin_unlock_irq(&wq->hash->wait.lock);
+ return ret;
}
/*
@@ -474,14 +477,21 @@ static struct io_wq_work *io_get_next_wo
}
if (stall_hash != -1U) {
+ bool unstalled;
+
/*
* Set this before dropping the lock to avoid racing with new
* work being added and clearing the stalled bit.
*/
wqe->flags |= IO_WQE_FLAG_STALLED;
raw_spin_unlock(&wqe->lock);
- io_wait_on_hash(wqe, stall_hash);
+ unstalled = io_wait_on_hash(wqe, stall_hash);
raw_spin_lock(&wqe->lock);
+ if (unstalled) {
+ wqe->flags &= ~IO_WQE_FLAG_STALLED;
+ if (wq_has_sleeper(&wqe->wq->hash->wait))
+ wake_up(&wqe->wq->hash->wait);
+ }
}
return NULL;
@@ -562,11 +572,14 @@ get_next:
io_wqe_enqueue(wqe, linked);
if (hash != -1U && !next_hashed) {
+ /* serialize hash clear with wake_up() */
+ spin_lock_irq(&wq->hash->wait.lock);
clear_bit(hash, &wq->hash->map);
+ wqe->flags &= ~IO_WQE_FLAG_STALLED;
+ spin_unlock_irq(&wq->hash->wait.lock);
if (wq_has_sleeper(&wq->hash->wait))
wake_up(&wq->hash->wait);
raw_spin_lock_irq(&wqe->lock);
- wqe->flags &= ~IO_WQE_FLAG_STALLED;
/* skip unnecessary unlock-lock wqe->lock */
if (!work)
goto get_next;
Patches currently in stable-queue which might be from axboe@xxxxxxxxx are
queue-5.14/floppy-fix-add_disk-assumption-on-exit-due-to-new-de.patch
queue-5.14/block-ataflop-more-blk-mq-refactoring-fixes.patch
queue-5.14/nbd-fix-use-after-free-in-pid_show.patch
queue-5.14/floppy-use-blk_cleanup_disk.patch
queue-5.14/block-ataflop-use-the-blk_cleanup_disk-helper.patch
queue-5.14/md-update-superblock-after-changing-rdev-flags-in-st.patch
queue-5.14/alsa-hda-reduce-udelay-at-skl-position-reporting.patch
queue-5.14/block-ataflop-add-registration-bool-before-calling-d.patch
queue-5.14/md-raid1-only-allocate-write-behind-bio-for-writemostly-device.patch
queue-5.14/ataflop-remove-ataflop_probe_lock-mutex.patch
queue-5.14/block-remove-inaccurate-requeue-check.patch
queue-5.14/block-ataflop-provide-a-helper-for-cleanup-up-an-ata.patch
queue-5.14/floppy-fix-calling-platform_device_unregister-on-inv.patch
queue-5.14/io-wq-ensure-that-hash-wait-lock-is-irq-disabling.patch
queue-5.14/block-schedule-queue-restart-after-blk_sts_zone_reso.patch
queue-5.14/io-wq-fix-queue-stalling-race.patch
queue-5.14/block-ataflop-fix-breakage-introduced-at-blk-mq-refa.patch
queue-5.14/io-wq-serialize-hash-clear-with-wakeup.patch
queue-5.14/nvdimm-btt-do-not-call-del_gendisk-if-not-needed.patch
queue-5.14/blk-cgroup-synchronize-blkg-creation-against-policy-.patch
queue-5.14/nbd-fix-possible-overflow-for-first_minor-in-nbd_dev.patch
queue-5.14/nbd-fix-max-value-for-first_minor.patch
queue-5.14/block-bump-max-plugged-deferred-size-from-16-to-32.patch
