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nfsd: don't call locks_release_private() twice concurrently

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[ Upstream commit 05eda6e75773592760285e10ac86c56d683be17f ]

It is possible for free_blocked_lock() to be called twice concurrently,
once from nfsd4_lock() and once from nfsd4_release_lockowner() calling
remove_blocked_locks().  This is why a kref was added.

It is perfectly safe for locks_delete_block() and kref_put() to be
called in parallel as they use locking or atomicity respectively as
protection.  However locks_release_private() has no locking.  It is
safe for it to be called twice sequentially, but not concurrently.

This patch moves that call from free_blocked_lock() where it could race
with itself, to free_nbl() where it cannot.  This will slightly delay
the freeing of private info or release of the owner - but not by much.
It is arguably more natural for this freeing to happen in free_nbl()
where the structure itself is freed.

This bug was found by code inspection - it has not been seen in practice.

Fixes: 47446d74f1 ("nfsd4: add refcount for nfsd4_blocked_lock")
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
NeilBrown 2024-08-26 11:07:02 -04:00 • committed by Greg Kroah-Hartman
parent 631e27be99
commit 3977ac0c22
1 changed files with 1 additions and 1 deletions
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2
fs/nfsd/nfs4state.c
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@ -318,6 +318,7 @@ free_nbl(struct kref *kref)
struct nfsd4_blocked_lock *nbl;
nbl = container_of(kref, struct nfsd4_blocked_lock, nbl_kref);
locks_release_private(&nbl->nbl_lock);
kfree(nbl);
}
@ -325,7 +326,6 @@ static void
free_blocked_lock(struct nfsd4_blocked_lock *nbl)
{
locks_delete_block(&nbl->nbl_lock);
locks_release_private(&nbl->nbl_lock);
kref_put(&nbl->nbl_kref, free_nbl);
}