ceph: fix leaked inode ref due to snap metadata writeback race
We create a ceph_cap_snap if there is dirty cap metadata (for writeback to
mds) OR dirty pages (for writeback to osd). It is thus possible that the
metadata has been written back to the MDS but the OSD data has not when
the cap_snap is created. This results in a cap_snap with dirty(caps) == 0.
The problem is that cap writeback to the MDS isn't necessary, and a
FLUSHSNAP cap op gets no ack from the MDS. This leaves the cap_snap
attached to the inode along with its inode reference.
Fix the problem by dropping the cap_snap if it becomes 'complete' (all
pages written out) and dirty(caps) == 0 in ceph_put_wrbuffer_cap_refs().
Also, BUG() in __ceph_flush_snaps() if we encounter a cap_snap with
dirty(caps) == 0.
Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 7d0a0d0..b6fdf01 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1204,6 +1204,12 @@
if (capsnap->dirty_pages || capsnap->writing)
continue;
+ /*
+ * if cap writeback already occurred, we should have dropped
+ * the capsnap in ceph_put_wrbuffer_cap_refs.
+ */
+ BUG_ON(capsnap->dirty == 0);
+
/* pick mds, take s_mutex */
mds = __ceph_get_cap_mds(ci, &mseq);
if (session && session->s_mds != mds) {
@@ -2117,8 +2123,8 @@
}
spin_unlock(&inode->i_lock);
- dout("put_cap_refs %p had %s %s\n", inode, ceph_cap_string(had),
- last ? "last" : "");
+ dout("put_cap_refs %p had %s%s%s\n", inode, ceph_cap_string(had),
+ last ? " last" : "", put ? " put" : "");
if (last && !flushsnaps)
ceph_check_caps(ci, 0, NULL);
@@ -2142,7 +2148,8 @@
{
struct inode *inode = &ci->vfs_inode;
int last = 0;
- int last_snap = 0;
+ int complete_capsnap = 0;
+ int drop_capsnap = 0;
int found = 0;
struct ceph_cap_snap *capsnap = NULL;
@@ -2165,19 +2172,32 @@
list_for_each_entry(capsnap, &ci->i_cap_snaps, ci_item) {
if (capsnap->context == snapc) {
found = 1;
- capsnap->dirty_pages -= nr;
- last_snap = !capsnap->dirty_pages;
break;
}
}
BUG_ON(!found);
+ capsnap->dirty_pages -= nr;
+ if (capsnap->dirty_pages == 0) {
+ complete_capsnap = 1;
+ if (capsnap->dirty == 0)
+ /* cap writeback completed before we created
+ * the cap_snap; no FLUSHSNAP is needed */
+ drop_capsnap = 1;
+ }
dout("put_wrbuffer_cap_refs on %p cap_snap %p "
- " snap %lld %d/%d -> %d/%d %s%s\n",
+ " snap %lld %d/%d -> %d/%d %s%s%s\n",
inode, capsnap, capsnap->context->seq,
ci->i_wrbuffer_ref+nr, capsnap->dirty_pages + nr,
ci->i_wrbuffer_ref, capsnap->dirty_pages,
last ? " (wrbuffer last)" : "",
- last_snap ? " (capsnap last)" : "");
+ complete_capsnap ? " (complete capsnap)" : "",
+ drop_capsnap ? " (drop capsnap)" : "");
+ if (drop_capsnap) {
+ ceph_put_snap_context(capsnap->context);
+ list_del(&capsnap->ci_item);
+ list_del(&capsnap->flushing_item);
+ ceph_put_cap_snap(capsnap);
+ }
}
spin_unlock(&inode->i_lock);
@@ -2185,10 +2205,12 @@
if (last) {
ceph_check_caps(ci, CHECK_CAPS_AUTHONLY, NULL);
iput(inode);
- } else if (last_snap) {
+ } else if (complete_capsnap) {
ceph_flush_snaps(ci);
wake_up(&ci->i_cap_wq);
}
+ if (drop_capsnap)
+ iput(inode);
}
/*
@@ -2464,8 +2486,8 @@
break;
}
WARN_ON(capsnap->dirty_pages || capsnap->writing);
- dout(" removing cap_snap %p follows %lld\n",
- capsnap, follows);
+ dout(" removing %p cap_snap %p follows %lld\n",
+ inode, capsnap, follows);
ceph_put_snap_context(capsnap->context);
list_del(&capsnap->ci_item);
list_del(&capsnap->flushing_item);