ceph_add_cap says in its function documentation that the caller should
hold the read lock on the session snap_rwsem. Furthermore, not only
ceph_add_cap needs that lock, when it calls to ceph_lookup_snap_realm it
eventually calls ceph_get_snap_realm which states via lockdep that
snap_rwsem needs to be held. handle_cap_export calls ceph_add_cap
without that mdsc->snap_rwsem held. Thus, since ceph_get_snap_realm
and ceph_add_cap both need the lock, the common place to acquire that
lock is inside handle_cap_export.
Signed-off-by: Niels Dossche <dossche.niels@xxxxxxxxx>
---
fs/ceph/caps.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index b472cd066d1c..0dd60db285b1 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -3903,8 +3903,10 @@ static void handle_cap_export(struct inode *inode, struct ceph_mds_caps *ex,
/* add placeholder for the export tagert */
int flag = (cap == ci->i_auth_cap) ? CEPH_CAP_FLAG_AUTH : 0;
tcap = new_cap;
+ down_read(&mdsc->snap_rwsem);
ceph_add_cap(inode, tsession, t_cap_id, issued, 0,
t_seq - 1, t_mseq, (u64)-1, flag, &new_cap);
+ up_read(&mdsc->snap_rwsem);
if (!list_empty(&ci->i_cap_flush_list) &&
ci->i_auth_cap == tcap) {
--
2.35.1
