5.15-stable review patch. If anyone has any objections, please let me know.
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From: NeilBrown neilb@suse.de
[ 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: 47446d74f170 ("nfsd4: add refcount for nfsd4_blocked_lock") Signed-off-by: NeilBrown neilb@suse.de Signed-off-by: Chuck Lever chuck.lever@oracle.com --- 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 0f1ece95bd642..ccc235a8bc1b4 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); }