[PATCH] nfsd: don't put blocked locks on LRU until after vfs_lock_file returns

[Jeff Layton <jlayton@kernel.org>]

Vasily reported a case where vfs_lock_file took a very long time to
return (longer than a lease period). The laundromat eventually ran and
reaped the thing and when the vfs_lock_file returned, it ended up
accessing freed memory.

Don't put entries onto the LRU until vfs_lock_file returns.

Reported-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfs4state.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index bfad94c70b84..8cfef84b9355 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -6966,10 +6966,8 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	}
 
 	if (fl_flags & FL_SLEEP) {
-		nbl->nbl_time = ktime_get_boottime_seconds();
 		spin_lock(&nn->blocked_locks_lock);
 		list_add_tail(&nbl->nbl_list, &lock_sop->lo_blocked);
-		list_add_tail(&nbl->nbl_lru, &nn->blocked_locks_lru);
 		spin_unlock(&nn->blocked_locks_lock);
 	}
 
@@ -6982,6 +6980,10 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 			nn->somebody_reclaimed = true;
 		break;
 	case FILE_LOCK_DEFERRED:
+		nbl->nbl_time = ktime_get_boottime_seconds();
+		spin_lock(&nn->blocked_locks_lock);
+		list_add_tail(&nbl->nbl_lru, &nn->blocked_locks_lru);
+		spin_unlock(&nn->blocked_locks_lock);
 		nbl = NULL;
 		fallthrough;
 	case -EAGAIN:		/* conflock holds conflicting lock */
-- 
2.33.1