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, 17 insertions, 3 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index ba5bbf318fe1..a2069b6680ae 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1143,6 +1143,10 @@ static int __send_cap(struct ceph_mds_client *mdsc, struct ceph_cap *cap,
 		for (i = 0; i < CEPH_CAP_BITS; i++)
 			if (flushing & (1 << i))
 				ci->i_cap_flush_tid[i] = flush_tid;
+
+		follows = ci->i_head_snapc->seq;
+	} else {
+		follows = 0;
 	}
 
 	keep = cap->implemented;
@@ -1156,7 +1160,6 @@ static int __send_cap(struct ceph_mds_client *mdsc, struct ceph_cap *cap,
 	mtime = inode->i_mtime;
 	atime = inode->i_atime;
 	time_warp_seq = ci->i_time_warp_seq;
-	follows = ci->i_snap_realm->cached_context->seq;
 	uid = inode->i_uid;
 	gid = inode->i_gid;
 	mode = inode->i_mode;
@@ -1332,7 +1335,11 @@ void __ceph_mark_dirty_caps(struct ceph_inode_info *ci, int mask)
 	     ceph_cap_string(was | mask));
 	ci->i_dirty_caps |= mask;
 	if (was == 0) {
-		dout(" inode %p now dirty\n", &ci->vfs_inode);
+		if (!ci->i_head_snapc)
+			ci->i_head_snapc = ceph_get_snap_context(
+				ci->i_snap_realm->cached_context);
+		dout(" inode %p now dirty snapc %p\n", &ci->vfs_inode,
+			ci->i_head_snapc);
 		BUG_ON(!list_empty(&ci->i_dirty_item));
 		spin_lock(&mdsc->cap_dirty_lock);
 		list_add(&ci->i_dirty_item, &mdsc->cap_dirty);
@@ -2190,7 +2197,9 @@ void ceph_put_wrbuffer_cap_refs(struct ceph_inode_info *ci, int nr,
 
 	if (ci->i_head_snapc == snapc) {
 		ci->i_wrbuffer_ref_head -= nr;
-		if (!ci->i_wrbuffer_ref_head) {
+		if (ci->i_wrbuffer_ref_head == 0 &&
+		    ci->i_dirty_caps == 0 && ci->i_flushing_caps == 0) {
+			BUG_ON(!ci->i_head_snapc);
 			ceph_put_snap_context(ci->i_head_snapc);
 			ci->i_head_snapc = NULL;
 		}
@@ -2483,6 +2492,11 @@ static void handle_cap_flush_ack(struct inode *inode, u64 flush_tid,
 			dout(" inode %p now clean\n", inode);
 			BUG_ON(!list_empty(&ci->i_dirty_item));
 			drop = 1;
+			if (ci->i_wrbuffer_ref_head == 0) {
+				BUG_ON(!ci->i_head_snapc);
+				ceph_put_snap_context(ci->i_head_snapc);
+				ci->i_head_snapc = NULL;
+			}
 		} else {
 			BUG_ON(list_empty(&ci->i_dirty_item));
 		}