Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757272AbXHXUE4 (ORCPT ); Fri, 24 Aug 2007 16:04:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750952AbXHXUEr (ORCPT ); Fri, 24 Aug 2007 16:04:47 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:47977 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750877AbXHXUEq (ORCPT ); Fri, 24 Aug 2007 16:04:46 -0400 Message-ID: <46CF3988.1020408@us.ibm.com> Date: Fri, 24 Aug 2007 13:03:20 -0700 From: Sukadev Bhattiprolu User-Agent: Thunderbird 2.0.0.6 (Windows/20070728) MIME-Version: 1.0 To: Oleg Nesterov CC: taoyue , Andrew Morton , Alexey Dobriyan , Ingo Molnar , Thomas Gleixner , Roland McGrath , linux-kernel@vger.kernel.org, stable@kernel.org Subject: Re: [PATCH] sigqueue_free: fix the race with collect_signal() References: <20070823134538.GA1358@tv-sign.ru> <46CEEA94.2070902@windriver.com> <20070824074558.GA86@tv-sign.ru> <46CF4DCB.6030304@windriver.com> <20070824110836.GA74@tv-sign.ru> In-Reply-To: <20070824110836.GA74@tv-sign.ru> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2608 Lines: 74 Oleg Nesterov wrote: > On 08/24, taoyue wrote: > >> Oleg Nesterov wrote: >> >>>> collect_signal: sigqueue_free: >>>> >>>> list_del_init(&first->list); >>>> spin_lock_irqsave(lock, flags); >>>> >>>> >>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >>> >>> >>>> if (!list_empty(&q->list)) >>>> list_del_init(&q->list); >>>> spin_unlock_irqrestore(lock, >>>> flags); >>>> q->flags &= ~SIGQUEUE_PREALLOC; >>>> >>>> __sigqueue_free(first); __sigqueue_free(q); >>>> >>>> >>> collect_signal() is always called under ->siglock which is also taken by >>> sigqueue_free(), so this is not possible. >>> >>> Basically, this patch is the same one-liner I sent you before >>> >>> http://marc.info/?l=linux-kernel&m=118772206603453&w=2 >>> >>> (Thanks for the additional testing and report, btw). >>> >>> P.S. It would be nice to know if this patch solves the problems reported >>> by Jeremy, but his email is disabled. >>> >>> Oleg. >>> >>> >>> >> I know, using current->sighand->siglock to prevent one sigqueue >> is free twice. I want to know whether it is possible that the two >> function is called in different thread. If that, the spin_lock is useless. >> > > Not sure I understand. Yes, it is possible they are called by 2 different > threads, that is why we had a race. But all threads in the same thread > group have the same ->sighand, and thus the same ->sighand->siglock. > Oleg, if one thread can be in collect_signal() and another in sigqueue_free() and both operate on the exact same sigqueue object, its not clear how we prevent two calls to __sigqueue_free() to the same object. In that case the lock (or some lock) should be around __sigqueue_free() - no ? i.e if we enter sigqueue_free(), we will call __sigqueue_free() regardless of the state. > Oleg. > > - > 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/ > > - 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/