ceph: introduce global empty snap context
Current snaphost code does not properly handle moving inode from one
empty snap realm to another empty snap realm. After changing inode's
snap realm, some dirty pages' snap context can be not equal to inode's
i_head_snap. This can trigger BUG() in ceph_put_wrbuffer_cap_refs()
The fix is introduce a global empty snap context for all empty snap
realm. This avoids triggering the BUG() for filesystem with no snapshot.
Fixes: http://tracker.ceph.com/issues/9928
Signed-off-by: Yan, Zheng <zyan@redhat.com>
Reviewed-by: Ilya Dryomov <idryomov@redhat.com>
diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index c1cc993..f64576e 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -288,6 +288,9 @@
return 0;
}
+
+static struct ceph_snap_context *empty_snapc;
+
/*
* build the snap context for a given realm.
*/
@@ -328,6 +331,12 @@
return 0;
}
+ if (num == 0 && realm->seq == empty_snapc->seq) {
+ ceph_get_snap_context(empty_snapc);
+ snapc = empty_snapc;
+ goto done;
+ }
+
/* alloc new snap context */
err = -ENOMEM;
if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
@@ -365,6 +374,7 @@
realm->ino, realm, snapc, snapc->seq,
(unsigned int) snapc->num_snaps);
+done:
ceph_put_snap_context(realm->cached_context);
realm->cached_context = snapc;
return 0;
@@ -465,6 +475,9 @@
cap_snap. lucky us. */
dout("queue_cap_snap %p already pending\n", inode);
kfree(capsnap);
+ } else if (ci->i_snap_realm->cached_context == empty_snapc) {
+ dout("queue_cap_snap %p empty snapc\n", inode);
+ kfree(capsnap);
} else if (dirty & (CEPH_CAP_AUTH_EXCL|CEPH_CAP_XATTR_EXCL|
CEPH_CAP_FILE_EXCL|CEPH_CAP_FILE_WR)) {
struct ceph_snap_context *snapc = ci->i_head_snapc;
@@ -925,5 +938,16 @@
return;
}
+int __init ceph_snap_init(void)
+{
+ empty_snapc = ceph_create_snap_context(0, GFP_NOFS);
+ if (!empty_snapc)
+ return -ENOMEM;
+ empty_snapc->seq = 1;
+ return 0;
+}
-
+void ceph_snap_exit(void)
+{
+ ceph_put_snap_context(empty_snapc);
+}