Re: User process NFS write hang followed by automount hang requiring reboot

[bfields@fieldses.org (J. Bruce Fields)]

On Tue, May 21, 2019 at 01:22:54PM -0600, Alan Post wrote:
> On Tue, May 21, 2019 at 03:46:03PM +0000, Trond Myklebust wrote:
> > > A representative sample of stack traces from hung user-submitted
> > > processes (jobs).  The first here is quite a lot more common than
> > > the later two:
> > > 
> > >     $ sudo cat /proc/197520/stack
> > >     [<0>] io_schedule+0x12/0x40
> > >     [<0>] nfs_lock_and_join_requests+0x309/0x4c0 [nfs]
> > >     [<0>] nfs_updatepage+0x2a2/0x8b0 [nfs]
> > >     [<0>] nfs_write_end+0x63/0x4c0 [nfs]
> > >     [<0>] generic_perform_write+0x138/0x1b0
> > >     [<0>] nfs_file_write+0xdc/0x200 [nfs]
> > >     [<0>] new_sync_write+0xfb/0x160
> > >     [<0>] vfs_write+0xa5/0x1a0
> > >     [<0>] ksys_write+0x4f/0xb0
> > >     [<0>] do_syscall_64+0x53/0x100
> > >     [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > >     [<0>] 0xffffffffffffffff
> > > 
> > 
> > Have you tried upgrading to 4.19.44? There is a fix that went in not
> > too long ago that deals with a request leak that can cause stack traces
> > like the above that wait forever.
> > 
> 
> That I haven't tried.  I gather you're talking about either or both
> of:
> 
>     63b0ee126f7e
>     be74fddc976e
> 
> Which I do see went in after 4.19.24 (which I've tried) but didn't
> get in 4.20.9 (which I've also tried).  Let me see about trying the
> 4.19.44 kernel.
> 
> > By the way, the above stack trace with "nfs_lock_and_join_requests"
> > usually means that you are using a very small rsize or wsize (less than
> > 4k). Is that the case? If so, you might want to look into just
> > increasing the I/O size.
> > 
> 
> These exports have rsize and wsize set to 1048576.

Are you getting that from the mount commandline?  It could be negotiated
down during mount.  I think you can get the negotiated values form the
rsize= and wsize= values on the opts: line in /proc/self/mountstats.
See also /proc/fs/nfsd/max_block_size.

--b.

> That decision was
> before my time, and I'll guess this value was picked to match
> NFSSVC_MAXBLKSIZE.
> 
> Thank you for your help,
> 
> -A
> -- 
> Alan Post | Xen VPS hosting for the technically adept
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