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SUNRPC: fix races on PipeFS UMOUNT notifications

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CPU#0                                   CPU#1
-----------------------------           -----------------------------
rpc_kill_sb
sn->pipefs_sb = NULL                    rpc_release_client
(UMOUNT_EVENT)                          rpc_free_auth
rpc_pipefs_event
rpc_get_client_for_event
!atomic_inc_not_zero(cl_count)
<skip the client>
                                        atomic_inc(cl_count)
                                        rpc_free_client
                                        rpc_clnt_remove_pipedir
                                        <skip client dir removing>

To fix this, this patch does the following:

1) Calls RPC_PIPEFS_UMOUNT notification with sn->pipefs_sb_lock being held.
2) Removes SUNRPC client from the list AFTER pipes destroying.
3) Doesn't hold RPC client on notification: if client in the list, then it
can't be destroyed while sn->pipefs_sb_lock in hold by notification caller.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: stable@vger.kernel.org
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
This commit is contained in:
Stanislav Kinsbursky
2013-06-26 10:15:14 +04:00
committed by Trond Myklebust
parent 384816051c
commit adb6fa7ffe
2 changed files with 2 additions and 5 deletions
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2
net/sunrpc/rpc_pipe.c
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@@ -1166,12 +1166,12 @@ static void rpc_kill_sb(struct super_block *sb)
goto out;
}
sn->pipefs_sb = NULL;
mutex_unlock(&sn->pipefs_sb_lock);
dprintk("RPC: sending pipefs UMOUNT notification for net %p%s\n",
net, NET_NAME(net));
blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
RPC_PIPEFS_UMOUNT,
sb);
mutex_unlock(&sn->pipefs_sb_lock);
put_net(net);
out:
kill_litter_super(sb);