From: Dave Chinner <david@fromorbit.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>,
Linux MM <linux-mm@kvack.org>,
linux-nvdimm <linux-nvdimm@lists.01.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
"Barror, Robert" <robert.barror@intel.com>
Subject: Re: Hang / zombie process from Xarray page-fault conversion (bisected)
Date: Tue, 12 Mar 2019 15:37:54 +1100 [thread overview]
Message-ID: <20190312043754.GD23020@dastard> (raw)
In-Reply-To: <CAPcyv4jG5r2LOesxSx+Mdf+L_gQWqnhk+gKZyKAAPTHy1Drvqw@mail.gmail.com>
On Mon, Mar 11, 2019 at 08:35:05PM -0700, Dan Williams wrote:
> On Mon, Mar 11, 2019 at 8:10 AM Matthew Wilcox <willy@infradead.org> 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
next prev parent reply other threads:[~2019-03-12 4:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-08 6:16 Hang / zombie process from Xarray page-fault conversion (bisected) Dan Williams
2019-03-11 15:09 ` Matthew Wilcox
2019-03-12 3:35 ` Dan Williams
2019-03-12 4:37 ` Dave Chinner [this message]
2019-03-12 16:53 ` Barror, Robert
2019-03-14 7:34 ` Dan Williams
2019-03-15 2:26 ` Dave Chinner
2019-03-15 2:46 ` Dan Williams
2019-05-04 19:42 ` Matthew Wilcox
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