From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752590Ab1HQMHA (ORCPT ); Wed, 17 Aug 2011 08:07:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37678 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751898Ab1HQMG7 (ORCPT ); Wed, 17 Aug 2011 08:06:59 -0400 Date: Wed, 17 Aug 2011 14:04:05 +0200 From: Oleg Nesterov To: Matt Fleming Cc: linux-kernel@vger.kernel.org, Petr Vandrovec , Al Viro , Arnd Bergmann Subject: Re: [PATCH 40/41] ncpfs: Use set_current_blocked() Message-ID: <20110817120405.GA10709@redhat.com> References: <1313071035-12047-1-git-send-email-matt@console-pimps.org> <1313071035-12047-41-git-send-email-matt@console-pimps.org> <20110816175643.GI29190@redhat.com> <1313528170.3436.200.camel@mfleming-mobl1.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1313528170.3436.200.camel@mfleming-mobl1.ger.corp.intel.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/16, Matt Fleming wrote: > > On Tue, 2011-08-16 at 19:56 +0200, Oleg Nesterov wrote: > > On 08/11, Matt Fleming wrote: > > > > > > As described in e6fa16ab ("signal: sigprocmask() should do > > > retarget_shared_pending()") the modification of current->blocked is > > > incorrect as we need to check whether the signal we're about to block > > > is pending in the shared queue. > > > > I'd wish I could understand this code but this seems impossible ;) > > Yeah, I gave up after staring at it for about twenty minutes. I couldn't > fathom the logic behind it. > > > IOW, "This doesn't seem right at all." looks reasonable, and the > > PF_EXITING adds even more confusion. > > Definitely. If I was more confident in this area of the kernel I would > have just deleted it ;-) Same here ;) > Because the thread doesn't hold ->siglock over do_ncp_rpc_call() another > thread could change the signal handler for SIGINT or SIGQUIT mid-call. > Which makes the code under "if (server->m.flags & NCP_MOUNT_INTR)" > pointless. (indeed, and see below) > > Why do we take ->siglock in the first place? > > > > I think it is not needed. We can calculate mask/blocked lockless and > > use set_task_blocked(). This also makes sense because __set_task_blocked > > is not exported ;) > > Eek! Sorry, I didn't realise this didn't compile. > > > the sighand->action[] checks are racy anyway in the mt case, siglock > > can't help. > > Hmm.. really? I thought that ->siglock serialised modifications to > sighand->action[] even in the mt case, no? Sure. But another thread can change sighand->action[] right after we drop ->siglock. So how can this lock help? We simply read the word, this is atomic and doesn't need the locking. Oleg.