ceph: take snap_rwsem when accessing snap realm's cached_context

When ceph inode's i_head_snapc is NULL, __ceph_mark_dirty_caps()
accesses snap realm's cached_context. So we need take read lock
of snap_rwsem.

Signed-off-by: Yan, Zheng <zyan@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index f1dbcae7c75c..900c05fd77d8 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1413,9 +1413,11 @@ int __ceph_mark_dirty_caps(struct ceph_inode_info *ci, int mask)
              ceph_cap_string(was | mask));
         ci->i_dirty_caps |= mask;
         if (was == 0) {
-                if (!ci->i_head_snapc)
+                if (!ci->i_head_snapc) {
+                        WARN_ON_ONCE(!rwsem_is_locked(&mdsc->snap_rwsem));
                         ci->i_head_snapc = ceph_get_snap_context(
                                 ci->i_snap_realm->cached_context);
+                }
                 dout(" inode %p now dirty snapc %p auth cap %p\n",
                      &ci->vfs_inode, ci->i_head_snapc, ci->i_auth_cap);
                 BUG_ON(!list_empty(&ci->i_dirty_item));