From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH] Describe race of direct read and fork for unaligned buffers Date: Wed, 2 May 2012 11:20:29 +0200 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 Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Hugh Dickins Cc: Nick Piggin , mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, KOSAKI Motohiro , Jan Kara , LKML , linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, mgorman-l3A5Bk7waGM@public.gmane.org, Jeff Moyer List-Id: linux-man@vger.kernel.org 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 from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html