11:46 a.m.
On Thu, Mar 14, 2019 at 7:26 PM Dave Chinner <david(a)fromorbit.com> wrote:
On Thu, Mar 14, 2019 at 12:34:51AM -0700, Dan Williams wrote:
> On Mon, Mar 11, 2019 at 9:38 PM Dave Chinner <david(a)fromorbit.com> wrote:
> >
> > 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(a)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.
>
> Here it is:
>
> https://gist.github.com/djbw/ca7117023305f325aca6f8ef30e11556
Which tells us nothing. :(
I think a bisect is in order...
Right, you missed this earlier in the thread, bisect points to:
b15cd800682f "dax: Convert page fault handlers to XArray"