ceph: fix snap writeback when racing with writes
There are two problems that come up when we try to queue a capsnap while a
write is in progress:
- The FILE_WR cap is held, but not yet dirty, so we may queue a capsnap
with dirty == 0. That will crash later in __ceph_flush_snaps(). Or
on the FILE_WR cap if a write is in progress.
- We may not have i_head_snapc set, which causes problems pretty quickly.
Look to the snaprealm in this case.
Reviewed-by: Yehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index 54b14de..ac030c9 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -449,6 +449,15 @@
spin_lock(&inode->i_lock);
used = __ceph_caps_used(ci);
dirty = __ceph_caps_dirty(ci);
+
+ /*
+ * If there is a write in progress, treat that as a dirty Fw,
+ * even though it hasn't completed yet; by the time we finish
+ * up this capsnap it will be.
+ */
+ if (used & CEPH_CAP_FILE_WR)
+ dirty |= CEPH_CAP_FILE_WR;
+
if (__ceph_have_pending_cap_snap(ci)) {
/* there is no point in queuing multiple "pending" cap_snaps,
as no new writes are allowed to start when pending, so any
@@ -456,14 +465,22 @@
cap_snap. lucky us. */
dout("queue_cap_snap %p already pending\n", inode);
kfree(capsnap);
- } else if (ci->i_wrbuffer_ref_head || (used & CEPH_CAP_FILE_WR) ||
+ } else if (ci->i_wrbuffer_ref_head ||
(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;
- dout("queue_cap_snap %p cap_snap %p queuing under %p\n", inode,
- capsnap, snapc);
+ /*
+ * if we are a sync write, we may need to go to the snaprealm
+ * to get the current snapc.
+ */
+ if (!snapc)
+ snapc = ci->i_snap_realm->cached_context;
+
+ dout("queue_cap_snap %p cap_snap %p queuing under %p %s\n",
+ inode, capsnap, snapc, ceph_cap_string(dirty));
ihold(inode);
+ BUG_ON(dirty == 0);
atomic_set(&capsnap->nref, 1);
capsnap->ci = ci;