From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx145.postini.com [74.125.245.145]) by kanga.kvack.org (Postfix) with SMTP id C4BBB6B004D for ; Wed, 2 May 2012 05:20:36 -0400 (EDT) Date: Wed, 2 May 2012 11:20:29 +0200 From: Jan Kara Subject: Re: [PATCH] Describe race of direct read and fork for unaligned buffers Message-ID: <20120502092029.GD16976@quack.suse.cz> References: <1335778207-6511-1-git-send-email-jack@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Nick Piggin , mtk.manpages@gmail.com, KOSAKI Motohiro , Jan Kara , LKML , linux-man@vger.kernel.org, linux-mm@kvack.org, mgorman@suse.de, Jeff Moyer On Tue 01-05-12 20:04:15, Hugh Dickins wrote: > On Wed, 2 May 2012, Nick Piggin wrote: > > On 2 May 2012 03:56, Michael Kerrisk (man-pages) wrote: > > > > > > In the light of all of the comments, can someone revise the man-pages > > > patch that Jan sent? > > > > This does not quite describe the entire situation, but something understandable > > to developers: > > > > O_DIRECT IOs should never be run concurrently with fork(2) system call, > > when the memory buffer is anonymous memory, or comes from mmap(2) > > with MAP_PRIVATE. > > > > Any such IOs, whether submitted with asynchronous IO interface or from > > another thread in the process, should be quiesced before fork(2) is called. > > Failure to do so can result in data corruption and undefined behavior in > > parent and child processes. > > > > This restriction does not apply when the memory buffer for the O_DIRECT > > IOs comes from mmap(2) with MAP_SHARED or from shmat(2). > > Nor does this restriction apply when the memory buffer has been advised > as MADV_DONTFORK with madvise(2), ensuring that it will not be available > to the child after fork(2). Yes, I think with this addition the text is fine. Honza -- Jan Kara SUSE Labs, CR -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org