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Subject[PATCH] ceph: Fix a memory leak in ci->i_head_snapc
Date
I'm occasionally seeing a kmemleak warning in xfstest generic/013:

unreferenced object 0xffff8881fccca940 (size 32):
comm "kworker/0:1", pid 12, jiffies 4295005883 (age 130.648s)
hex dump (first 32 bytes):
01 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<00000000d741a1ea>] build_snap_context+0x5b/0x2a0
[<0000000021a00533>] rebuild_snap_realms+0x27/0x90
[<00000000ac538600>] rebuild_snap_realms+0x42/0x90
[<000000000e955fac>] ceph_update_snap_trace+0x2ee/0x610
[<00000000a9550416>] ceph_handle_snap+0x317/0x5f3
[<00000000fc287b83>] dispatch+0x362/0x176c
[<00000000a312c741>] ceph_con_workfn+0x9ce/0x2cf0
[<000000004168e3a9>] process_one_work+0x1d4/0x400
[<000000002188e9e7>] worker_thread+0x2d/0x3c0
[<00000000b593e4b3>] kthread+0x112/0x130
[<00000000a8587dca>] ret_from_fork+0x35/0x40
[<00000000ba1c9c1d>] 0xffffffffffffffff

It looks like it is possible that we miss a flush_ack from the MDS when,
for example, umounting the filesystem. In that case, we can simply drop
the reference to the ceph_snap_context obtained in ceph_queue_cap_snap().

Link: https://tracker.ceph.com/issues/38224
Cc: stable@vger.kernel.org
Signed-off-by: Luis Henriques <lhenriques@suse.com>
---
fs/ceph/caps.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 36a8dc699448..208f4dc6f574 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1054,6 +1054,7 @@ int ceph_is_any_caps(struct inode *inode)
static void drop_inode_snap_realm(struct ceph_inode_info *ci)
{
struct ceph_snap_realm *realm = ci->i_snap_realm;
+
spin_lock(&realm->inodes_with_caps_lock);
list_del_init(&ci->i_snap_realm_item);
ci->i_snap_realm_counter++;
@@ -1063,6 +1064,12 @@ static void drop_inode_snap_realm(struct ceph_inode_info *ci)
spin_unlock(&realm->inodes_with_caps_lock);
ceph_put_snap_realm(ceph_sb_to_client(ci->vfs_inode.i_sb)->mdsc,
realm);
+ /*
+ * ci->i_head_snapc should be NULL, but we may still be waiting for a
+ * flush_ack from the MDS. In that case, we still hold a ref for the
+ * ceph_snap_context and we need to drop it.
+ */
+ ceph_put_snap_context(ci->i_head_snapc);
}

/*
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