From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763413AbXGMTyk (ORCPT ); Fri, 13 Jul 2007 15:54:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757056AbXGMTyd (ORCPT ); Fri, 13 Jul 2007 15:54:33 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:50287 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751303AbXGMTyd (ORCPT ); Fri, 13 Jul 2007 15:54:33 -0400 Subject: Re: [PATCH] Simplify /proc//exe symlink code From: Matt Helsley To: Andrew Morton Cc: Chris Wright , Al Viro , linux-mm@kvack.org, LKML , Christoph Hellwig , "Hallyn, Serge" , Peter Zijlstra In-Reply-To: <20070712192114.bb357ce4.akpm@linux-foundation.org> References: <1184292012.13479.14.camel@localhost.localdomain> <20070712192114.bb357ce4.akpm@linux-foundation.org> Content-Type: text/plain Organization: IBM Linux Technology Center Date: Fri, 13 Jul 2007 12:54:20 -0700 Message-Id: <1184356460.16131.4.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2007-07-12 at 19:21 -0700, Andrew Morton wrote: > On Thu, 12 Jul 2007 19:00:12 -0700 Matt Helsley wrote: > > > This patch avoids holding the mmap semaphore while walking VMAs in response to > > programs which read or follow the /proc//exe symlink. This also allows > > us to merge mmu and nommu proc_exe_link() functions. The costs are holding the > > task lock, a separate reference to the executable file stored in the task > > struct, and increased code in fork, exec, and exit paths. > > > > Signed-off-by: Matt Helsley > > --- > > > > Changelog: > > > > Hold task_lock() while using task->exe_file. With this change I haven't > > been able to reproduce Chris Wright's Oops report: > > http://lkml.org/lkml/2007/5/31/34 > > I used a 4-way, x86 system running kernbench. I also tried a 4-way x86_64 > > system running pidof. I used oprofile during all runs but I could not > > reproduce Chris' Oops with the new patch. > > > > Compiled and passed simple tests for regressions when patched against a 2.6.20 > > and a 2.6.22 kernel. Regression tests included a variety of file operations on > > /proc//exe such as stat, lstat, open, close, readlink, and unlink. All > > produced the expected, baseline output results. > > > > Andrew, please consider this patch for inclusion in -mm. > > I wish we had a description of the bug which this fixes. That email of > Chris's is referencing code which diddles with task_struct.exe_file, but > your patch _adds_ task_struct.exe_file, so I am all confused. Chris was testing the patch. The patch isn't a bug fix so much as a failed attempt to remove one use of the mm's mmap lock. > Your patch does lots of fput()s under task_lock(), but fput() can sleep. Ack, you're right. > Plus what Al said. Yup. Thanks, -Matt Helsley