[PATCH 5.17 68/75] NFSD: Fix possible sleep during nfsd4_release_lockowner()

Greg Kroah-Hartman
2022-06-03T18:14:00Z

From: Chuck Lever <chuck.lever@oracle.com>

commit ce3c4ad7f4ce5db7b4f08a1e237d8dd94b39180b upstream.

nfsd4_release_lockowner() holds clp->cl_lock when it calls
check_for_locks(). However, check_for_locks() calls nfsd_file_get()
/ nfsd_file_put() to access the backing inode's flc_posix list, and
nfsd_file_put() can sleep if the inode was recently removed.

Let's instead rely on the stateowner's reference count to gate
whether the release is permitted. This should be a reliable
indication of locks-in-use since file lock operations and
->lm_get_owner take appropriate references, which are released
appropriately when file locks are removed.

Reported-by: Dai Ngo <dai.ngo@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/nfsd/nfs4state.c | 12 ++++--------
1 file changed, 4 insertions(+), 8 deletions(-)

--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -7330,16 +7330,12 @@ nfsd4_release_lockowner(struct svc_rqst
if (sop->so_is_open_owner || !same_owner_str(sop, owner))
continue;

- /* see if there are still any locks associated with it */
- lo = lockowner(sop);
- list_for_each_entry(stp, &sop->so_stateids, st_perstateowner) {
- if (check_for_locks(stp->st_stid.sc_file, lo)) {
- status = nfserr_locks_held;
- spin_unlock(&clp->cl_lock);
- return status;
- }
+ if (atomic_read(&sop->so_count) != 1) {
+ spin_unlock(&clp->cl_lock);
+ return nfserr_locks_held;
}

+ lo = lockowner(sop);
nfs4_get_stateowner(sop);
break;
}