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, 5 insertions, 1 deletions

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index 6bdbf3ae7082..4868b9dcac5a 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -458,6 +458,8 @@ void ceph_queue_cap_snap(struct ceph_inode_info *ci)
                              CEPH_CAP_FILE_EXCL|CEPH_CAP_FILE_WR))) {
                 struct ceph_snap_context *snapc = ci->i_head_snapc;
 
+                dout("queue_cap_snap %p cap_snap %p queuing under %p\n", inode,
+                     capsnap, snapc);
                 igrab(inode);
                 
                 atomic_set(&capsnap->nref, 1);
@@ -489,7 +491,9 @@ void ceph_queue_cap_snap(struct ceph_inode_info *ci)
                 capsnap->dirty_pages = ci->i_wrbuffer_ref_head;
                 ci->i_wrbuffer_ref_head = 0;
                 capsnap->context = snapc;
-                ci->i_head_snapc = NULL;
+                ci->i_head_snapc =
+                        ceph_get_snap_context(ci->i_snap_realm->cached_context);
+                dout(" new snapc is %p\n", ci->i_head_snapc);
                 list_add_tail(&capsnap->ci_item, &ci->i_cap_snaps);
 
                 if (used & CEPH_CAP_FILE_WR) {