Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754580Ab1B1OvN (ORCPT ); Mon, 28 Feb 2011 09:51:13 -0500 Received: from mss-uk.mssgmbh.com ([217.174.251.109]:41912 "EHLO mss-uk.mssgmbh.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754316Ab1B1OvM (ORCPT ); Mon, 28 Feb 2011 09:51:12 -0500 To: netdev@vger.kernel.org Cc: davem@davemloft.net, linux-kernel@vger.kernel.org Subject: [PATCH] net: fix multithreaded signal handling in unix recv routines User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) From: Rainer Weikusat Date: Mon, 28 Feb 2011 14:50:55 +0000 Message-ID: <877hck43hs.fsf@sapphire.mobileactivedefense.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2733 Lines: 73 From: Rainer Weikusat The unix_dgram_recvmsg and unix_stream_recvmsg routines in net/af_unix.c utilize mutex_lock(&u->readlock) calls in order to serialize read operations of multiple threads on a single socket. This implies that, if all n threads of a process block in an AF_UNIX recv call trying to read data from the same socket, one of these threads will be sleeping in state TASK_INTERRUPTIBLE and all others in state TASK_UNINTERRUPTIBLE. Provided that a particular signal is supposed to be handled by a signal handler defined by the process and that none of this threads is blocking the signal, the complete_signal routine in kernel/signal.c will select the 'first' such thread it happens to encounter when deciding which thread to notify that a signal is supposed to be handled and if this is one of the TASK_UNINTERRUPTIBLE threads, the signal won't be handled until the one thread not blocking on the u->readlock mutex is woken up because some data to process has arrived (if this ever happens). The included patch fixes this by changing mutex_lock to mutex_lock_interruptible and handling possible error returns in the same way interruptions are handled by the actual receive-code. Signed-off-by: Rainer Weikusat --- diff -urp net-2.6/net/unix/af_unix.c net-2.6-patched//net/unix/af_unix.c --- net-2.6/net/unix/af_unix.c 2011-02-16 22:19:43.338358559 +0000 +++ net-2.6-patched//net/unix/af_unix.c 2011-02-16 22:38:39.483543598 +0000 @@ -1724,7 +1724,11 @@ static int unix_dgram_recvmsg(struct kio msg->msg_namelen = 0; - mutex_lock(&u->readlock); + err = mutex_lock_interruptible(&u->readlock); + if (err) { + err = sock_intr_errno(sock_rcvtimeo(sk, noblock)); + goto out; + } skb = skb_recv_datagram(sk, flags, noblock, &err); if (!skb) { @@ -1864,7 +1868,11 @@ static int unix_stream_recvmsg(struct ki memset(&tmp_scm, 0, sizeof(tmp_scm)); } - mutex_lock(&u->readlock); + err = mutex_lock_interruptible(&u->readlock); + if (err) { + err = sock_intr_errno(timeo); + goto out; + } do { int chunk; @@ -1895,11 +1903,12 @@ static int unix_stream_recvmsg(struct ki timeo = unix_stream_data_wait(sk, timeo); - if (signal_pending(current)) { + if (signal_pending(current) + || mutex_lock_interruptible(&u->readlock)) { err = sock_intr_errno(timeo); goto out; } - mutex_lock(&u->readlock); + continue; unlock: unix_state_unlock(sk); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/