From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx124.postini.com [74.125.245.124]) by kanga.kvack.org (Postfix) with SMTP id BF8F36B005D for ; Thu, 3 Jan 2013 21:49:39 -0500 (EST) Date: Fri, 4 Jan 2013 02:49:36 +0000 From: Al Viro Subject: Re: [PATCH] mm: protect against concurrent vma expansion Message-ID: <20130104024935.GF4939@ZenIV.linux.org.uk> References: <1354344987-28203-1-git-send-email-walken@google.com> <20121203150110.39c204ff.akpm@linux-foundation.org> <20121203164322.b967d461.akpm@linux-foundation.org> <20121204144820.GA13916@google.com> <1355968594.1415.4.camel@kernel-VirtualBox> <1357260005.4930.6.camel@kernel.cn.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1357260005.4930.6.camel@kernel.cn.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Simon Jeons Cc: Michel Lespinasse , Andrew Morton , linux-mm@kvack.org, Rik van Riel , Hugh Dickins , linux-kernel@vger.kernel.org On Thu, Jan 03, 2013 at 06:40:05PM -0600, Simon Jeons wrote: > On Wed, 2012-12-19 at 19:01 -0800, Michel Lespinasse wrote: > > Hi Simon, > > > > On Wed, Dec 19, 2012 at 5:56 PM, Simon Jeons wrote: > > > One question. > > > > > > I found that mainly callsite of expand_stack() is #PF, but it holds > > > mmap_sem each time before call expand_stack(), how can hold a *shared* > > > mmap_sem happen? > > > > the #PF handler calls down_read(&mm->mmap_sem) before calling expand_stack. > > > > I think I'm just confusing you with my terminology; shared lock == > > read lock == several readers might hold it at once (I'd say they share > > it) > > Sorry for my late response. > > Since expand_stack() will modify vma, then why hold a read lock here? To prevent that vma being ripped out. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org