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[150.101.137.143]) by mx.google.com with ESMTP id q3si6764469pfh.235.2019.03.11.21.37.56 for ; Mon, 11 Mar 2019 21:37:57 -0700 (PDT) Received-SPF: neutral (google.com: 150.101.137.143 is neither permitted nor denied by best guess record for domain of david@fromorbit.com) client-ip=150.101.137.143; Authentication-Results: mx.google.com; spf=neutral (google.com: 150.101.137.143 is neither permitted nor denied by best guess record for domain of david@fromorbit.com) smtp.mailfrom=david@fromorbit.com Received: from ppp59-167-129-252.static.internode.on.net (HELO dastard) ([59.167.129.252]) by ipmail03.adl6.internode.on.net with ESMTP; 12 Mar 2019 15:07:57 +1030 Received: from dave by dastard with local (Exim 4.80) (envelope-from ) id 1h3ZAo-0000Tt-Fr; Tue, 12 Mar 2019 15:37:54 +1100 Date: Tue, 12 Mar 2019 15:37:54 +1100 From: Dave Chinner To: Dan Williams Cc: Matthew Wilcox , Linux MM , linux-nvdimm , linux-fsdevel , "Barror, Robert" Subject: Re: Hang / zombie process from Xarray page-fault conversion (bisected) Message-ID: <20190312043754.GD23020@dastard> References: <20190311150947.GD19508@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Mar 11, 2019 at 08:35:05PM -0700, Dan Williams wrote: > On Mon, Mar 11, 2019 at 8:10 AM Matthew Wilcox wrote: > > > > On Thu, Mar 07, 2019 at 10:16:17PM -0800, Dan Williams wrote: > > > Hi Willy, > > > > > > We're seeing a case where RocksDB hangs and becomes defunct when > > > trying to kill the process. v4.19 succeeds and v4.20 fails. Robert was > > > able to bisect this to commit b15cd800682f "dax: Convert page fault > > > handlers to XArray". > > > > > > I see some direct usage of xa_index and wonder if there are some more > > > pmd fixups to do? > > > > > > Other thoughts? > > > > I don't see why killing a process would have much to do with PMD > > misalignment. The symptoms (hanging on a signal) smell much more like > > leaving a locked entry in the tree. Is this easy to reproduce? Can you > > get /proc/$pid/stack for a hung task? > > It's fairly easy to reproduce, I'll see if I can package up all the > dependencies into something that fails in a VM. > > It's limited to xfs, no failure on ext4 to date. > > The hung process appears to be: > > kworker/53:1-xfs-sync/pmem0 That's completely internal to XFS. Every 30s the work is triggered and it either does a log flush (if the fs is active) or it syncs the superblock to clean the log and idle the filesystem. It has nothing to do with user processes, and I don't see why killing a process has any effect on what it does... > ...and then the rest of the database processes grind to a halt from there. > > Robert was kind enough to capture /proc/$pid/stack, but nothing interesting: > > [<0>] worker_thread+0xb2/0x380 > [<0>] kthread+0x112/0x130 > [<0>] ret_from_fork+0x1f/0x40 > [<0>] 0xffffffffffffffff Much more useful would be: # echo w > /proc/sysrq-trigger And post the entire output of dmesg. Cheers, Dave. -- Dave Chinner david@fromorbit.com