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);
+}
diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index f6e1237..3b5c1e3 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -1028,15 +1028,20 @@
ceph_flock_init();
ceph_xattr_init();
+ ret = ceph_snap_init();
+ if (ret)
+ goto out_xattr;
ret = register_filesystem(&ceph_fs_type);
if (ret)
- goto out_icache;
+ goto out_snap;
pr_info("loaded (mds proto %d)\n", CEPH_MDSC_PROTOCOL);
return 0;
-out_icache:
+out_snap:
+ ceph_snap_exit();
+out_xattr:
ceph_xattr_exit();
destroy_caches();
out:
@@ -1047,6 +1052,7 @@
{
dout("exit_ceph\n");
unregister_filesystem(&ceph_fs_type);
+ ceph_snap_exit();
ceph_xattr_exit();
destroy_caches();
}
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index aca2287..fc1c825 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -699,6 +699,8 @@
extern int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
struct ceph_cap_snap *capsnap);
extern void ceph_cleanup_empty_realms(struct ceph_mds_client *mdsc);
+extern int ceph_snap_init(void);
+extern void ceph_snap_exit(void);
/*
* a cap_snap is "pending" if it is still awaiting an in-progress