From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753257AbbFDJqG (ORCPT ); Thu, 4 Jun 2015 05:46:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34960 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752282AbbFDJpv (ORCPT ); Thu, 4 Jun 2015 05:45:51 -0400 Date: Thu, 4 Jun 2015 11:45:42 +0200 From: Milos Vyletel To: Ingo Molnar Cc: Peter Zijlstra , Paul Mackerras , Ingo Molnar , Arnaldo Carvalho de Melo , Jiri Olsa , Don Zickus , Andy Shevchenko , "Steven Rostedt (Red Hat)" , "open list:PERFORMANCE EVENT..." Subject: Re: [PATCH] perf tools: avoid possible race condition in copyfile Message-ID: <20150604094542.GB2351@lenivo.usersys.redhat.com> References: <1433407453-28739-1-git-send-email-milos@redhat.com> <20150604091100.GA19775@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150604091100.GA19775@gmail.com> Organization: Red Hat Czech s.r.o. User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 04, 2015 at 11:11:00AM +0200, Ingo Molnar wrote: > > * Milos Vyletel wrote: > > > Use unique temporary files when copying to buildid dir to prevent races > > in case multiple instances are trying to copy same file. This is done by > > > > - creating template in form /..XXXXXX where the suffix is > > used by mkstemp() to create unique file > > - change file mode > > - copy content > > - if successful link temp file to target file > > - unlink temp file > > > > At this point the only file left at target path should be the desired > > one either created by us or other instance if we raced. This should also > > prevent not yet fully copied files to be visible to to other perf > > instances that could try to parse them. > > > > On top of that slow_copyfile no longer needs to deal with file mode when > > creating file since temporary file is already created and mode is set. > > > > Signed-off-by: Milos Vyletel > > Ok, that looks nice! Thanks. > > Assuming it passes testing you can add my ack to it: > I did some testing myself by running perf record, archive and reading the data on other system as well as running perf buildid-cache on perf binary itself. I did revert fix from 0635b0f that to expose the race with EEXIST and my recreator test passed sucessfully. I've also added debug printfs in the code to really make sure the temporary files are created, exist and then are moved back. Everything worked as expected but this can surely use some more testing. > Acked-by: Ingo Molnar > > Is there any other place in tools/perf where we are using file locking or racy > shared access to the same file(s)? > There are two places in code I'm aware of which copy files and the both end up calling copyfile_mode that this patch modifies. Those places are build_id_cache__add_kcore kcore_copy kcore_copy__copy_file copyfile_mode build_id_cache__add_s copyfile copyfile_mode unless I'm missing something we should cover all cases. Milos