Re: [PATCH] ceph: Fix a memory leak in ci->i_head_snapc

[Yan, Zheng]

On Fri, Mar 15, 2019 at 7:13 PM Luis Henriques <lhenriques@xxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Luis Henriques <lhenriques@xxxxxxxx>
> ---
>  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);
>  }
>
>  /*

This does not seem right.  i_head_snapc is cleared when
(ci->i_wrbuffer_ref_head == 0 && ci->i_dirty_caps == 0 &&
ci->i_flushing_caps == 0) . Nothing do with dropping ci->i_snap_realm.
Did you see 'reconnect denied' during the test? If you did, the fix
should be in iterate_session_caps()