Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753399AbbL2MaB (ORCPT ); Tue, 29 Dec 2015 07:30:01 -0500 Received: from mail-wm0-f48.google.com ([74.125.82.48]:38275 "EHLO mail-wm0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752049AbbL2M36 (ORCPT ); Tue, 29 Dec 2015 07:29:58 -0500 From: Nicolai Stange To: "David S. Miller" Cc: Nicolai Stange , Eric Dumazet , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] net, socket, socket_wq: fix missing initialization of flags References: <87ege73bma.fsf@gmail.com> <1451323186.8255.5.camel@edumazet-glaptop2.roam.corp.google.com> Date: Tue, 29 Dec 2015 13:29:55 +0100 In-Reply-To: <1451323186.8255.5.camel@edumazet-glaptop2.roam.corp.google.com> (Eric Dumazet's message of "Mon, 28 Dec 2015 12:19:46 -0500") Message-ID: <87ziwtphdo.fsf_-_@gmail.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2466 Lines: 60 Fixes: ceb5d58b2170 ("net: fix sock_wake_async() rcu protection") Commit ceb5d58b2170 ("net: fix sock_wake_async() rcu protection") from the current 4.4 release cycle introduced a new flags member in struct socket_wq and moved SOCKWQ_ASYNC_NOSPACE and SOCKWQ_ASYNC_WAITDATA from struct socket's flags member into that new place. Unfortunately, the new flags field is never initialized properly, at least not for the struct socket_wq instance created in sock_alloc_inode(). One particular issue I encountered because of this is that my GNU Emacs failed to draw anything on my desktop -- i.e. what I got is a transparent window, including the title bar. Bisection lead to the commit mentioned above and further investigation by means of strace told me that Emacs is indeed speaking to my Xorg through an O_ASYNC AF_UNIX socket. This is reproducible 100% of times and the fact that properly initializing the struct socket_wq ->flags fixes the issue leads me to the conclusion that somehow SOCKWQ_ASYNC_WAITDATA got set in the uninitialized ->flags, preventing my Emacs from receiving any SIGIO's due to data becoming available and it got stuck. Make sock_alloc_inode() set the newly created struct socket_wq's ->flags member to zero. Signed-off-by: Nicolai Stange --- Changes to V1 (only commit message changes): - Uhm, I misread sock_wake_async(). The meaning of the flags is actually inverted. My Ghostmacs wasn't waiting for free send space, but some received data becoming available. This makes indeed more sense and I replaced "SOCKWQ_ASYNC_NOSPACE" by "SOCKWQ_ASYNC_WAITDATA" in my speculative explanation above. - Furthermore I fixed some minor grammar issues. Sorry for any inconvenience this late-night induced brainfart might have caused at your side... net/socket.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/socket.c b/net/socket.c index 29822d6..d730ef9 100644 --- a/net/socket.c +++ b/net/socket.c @@ -257,6 +257,7 @@ static struct inode *sock_alloc_inode(struct super_block *sb) } init_waitqueue_head(&wq->wait); wq->fasync_list = NULL; + wq->flags = 0; RCU_INIT_POINTER(ei->socket.wq, wq); ei->socket.state = SS_UNCONNECTED; -- 2.6.4 -- 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/