From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:33496 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754719AbaCNOoj (ORCPT ); Fri, 14 Mar 2014 10:44:39 -0400 Message-ID: <532315D0.7090805@fb.com> Date: Fri, 14 Mar 2014 10:44:32 -0400 From: Josef Bacik MIME-Version: 1.0 To: Wang Shilong CC: Subject: Re: [PATCH] Btrfs: remove transaction from send References: <1394739733-500-1-git-send-email-jbacik@fb.com> <892DD229-24DA-439C-B431-2761E51A9937@gmail.com> In-Reply-To: <892DD229-24DA-439C-B431-2761E51A9937@gmail.com> Content-Type: text/plain; charset="ISO-8859-1" Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 03/14/2014 09:13 AM, Wang Shilong wrote: >> Lets try this again. We can deadlock the box if we send on a box and try to >> write onto the same fs with the app that is trying to listen to the send pipe. >> This is because the writer could get stuck waiting for a transaction commit >> which is being blocked by the send. So fix this by making sure looking at the >> commit roots is always going to be consistent. We do this by keeping track of >> which roots need to have their commit roots swapped during commit, and then >> taking the commit_root_sem and swapping them all at once. Then make sure we >> take a read lock on the commit_root_sem in cases where we search the commit root >> to make sure we're always looking at a consistent view of the commit roots. >> Previously we had problems with this because we would swap a fs tree commit root >> and then swap the extent tree commit root independently which would cause the >> backref walking code to screw up sometimes. With this patch we no longer >> deadlock and pass all the weird send/receive corner cases. Thanks, > > Now btrfs send are alway searching commit root! Your codes only seems to protect backref codes, > it reduce transaction blocked but make it not safe as we have discussed before. > > I was trying to remember why we didn't like this solution before but I couldn't come up with anything. Apparently I haven't completely fixed the problem yet so stay tuned for what I do next ;). Thanks, Josef