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NFSv4/pNFS: Fix a race to wake on NFS_LAYOUT_DRAIN 

[ Upstream commit c01776287414ca43412d1319d2877cbad65444ac ]

We found a few different systems hung up in writeback waiting on the same
page lock, and one task waiting on the NFS_LAYOUT_DRAIN bit in
pnfs_update_layout(), however the pnfs_layout_hdr's plh_outstanding count
was zero.

It seems most likely that this is another race between the waiter and waker
similar to commit ed0172af5d ("SUNRPC: Fix a race to wake a sync task").
Fix it up by applying the advised barrier.

Fixes: 880265c77a ("pNFS: Avoid a live lock condition in pnfs_update_layout()")
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 8ca65fa71024a1767a59ffbc6a6e2278af84735e)
This commit is contained in:
Benjamin Coddington 2025-06-19 11:02:21 -04:00 committed by Wentao Guan
parent 64e2ebeb9e
commit da15cd3211
1 changed files with 3 additions and 1 deletions
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4
fs/nfs/pnfs.c
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@ -1930,8 +1930,10 @@ static void nfs_layoutget_begin(struct pnfs_layout_hdr *lo)
static void nfs_layoutget_end(struct pnfs_layout_hdr *lo)
{
if (atomic_dec_and_test(&lo->plh_outstanding) &&
test_and_clear_bit(NFS_LAYOUT_DRAIN, &lo->plh_flags))
test_and_clear_bit(NFS_LAYOUT_DRAIN, &lo->plh_flags)) {
smp_mb__after_atomic();
wake_up_bit(&lo->plh_flags, NFS_LAYOUT_DRAIN);
}
}
static bool pnfs_is_first_layoutget(struct pnfs_layout_hdr *lo)