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: 47446d74f170 ("nfsd4: add refcount for nfsd4_blocked_lock")
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
fs/nfsd/nfs4state.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index a66d66b9f769..12534e12dbb3 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -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);
}
--
2.43.0
