ceph: maintain i_head_snapc when any caps are dirty, not just for data

We used to use i_head_snapc to keep track of which snapc the current epoch
of dirty data was dirtied under.  It is used by queue_cap_snap to set up
the cap_snap.  However, since we queue cap snaps for any dirty caps, not
just for dirty file data, we need to keep a valid i_head_snapc anytime
we have dirty|flushing caps.  This fixes a NULL pointer deref in
queue_cap_snap when writing back dirty caps without data (e.g.,
snaptest-authwb.sh).

Signed-off-by: Sage Weil <sage@newdream.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 420d46974ec8..4cfce1ee31fa 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -87,7 +87,7 @@ static int ceph_set_page_dirty(struct page *page)
 
         /* dirty the head */
         spin_lock(&inode->i_lock);
-        if (ci->i_wrbuffer_ref_head == 0)
+        if (ci->i_head_snapc == NULL)
                 ci->i_head_snapc = ceph_get_snap_context(snapc);
         ++ci->i_wrbuffer_ref_head;
         if (ci->i_wrbuffer_ref == 0)
@@ -346,7 +346,7 @@ static struct ceph_snap_context *get_oldest_context(struct inode *inode,
                         break;
                 }
         }
-        if (!snapc && ci->i_head_snapc) {
+        if (!snapc && ci->i_wrbuffer_ref_head) {
                 snapc = ceph_get_snap_context(ci->i_head_snapc);
                 dout(" head snapc %p has %d dirty pages\n",
                      snapc, ci->i_wrbuffer_ref_head);