From: NeilBrown <neilb@suse.de>
Date: Thu, 31 Oct 2013 05:14:36 +0000 (+1100)
Subject: SUNRPC: close a rare race in xs_tcp_setup_socket.
X-Git-Tag: omap-for-v3.13/fixes-for-merge-window-take2~60^2~9
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=93dc41bdc5c853916610576c6b48a1704959c70d;p=pandora-kernel.git

SUNRPC: close a rare race in xs_tcp_setup_socket.

We have one report of a crash in xs_tcp_setup_socket.
The call path to the crash is:

  xs_tcp_setup_socket -> inet_stream_connect -> lock_sock_nested.

The 'sock' passed to that last function is NULL.

The only way I can see this happening is a concurrent call to
xs_close:

  xs_close -> xs_reset_transport -> sock_release -> inet_release

inet_release sets:
   sock->sk = NULL;
inet_stream_connect calls
   lock_sock(sock->sk);
which gets NULL.

All calls to xs_close are protected by XPRT_LOCKED as are most
activations of the workqueue which runs xs_tcp_setup_socket.
The exception is xs_tcp_schedule_linger_timeout.

So presumably the timeout queued by the later fires exactly when some
other code runs xs_close().

To protect against this we can move the cancel_delayed_work_sync()
call from xs_destory() to xs_close().

As xs_close is never called from the worker scheduled on
->connect_worker, this can never deadlock.

Signed-off-by: NeilBrown <neilb@suse.de>
[Trond: Make it safe to call cancel_delayed_work_sync() on AF_LOCAL sockets]
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
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