linux-kernel - Re: Killing process in D state on mount to dead NFS server. (when process is in fsync)

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Message-ID: <CAABAsM6dNYMus3GrrHiT82-kEb_hAftXnuhSx6SXeuq-E1+JLg@mail.gmail.com>
Date:	Fri, 1 Aug 2014 23:44:32 -0400
From:	Trond Myklebust <trondmy@...il.com>
To:	NeilBrown <neilb@...e.de>
Cc:	Jeff Layton <jlayton@...chiereds.net>,
	Ben Greear <greearb@...delatech.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: Killing process in D state on mount to dead NFS server. (when
 process is in fsync)

On Fri, Aug 1, 2014 at 11:19 PM, NeilBrown <neilb@...e.de> wrote:
> On Fri, 1 Aug 2014 22:55:42 -0400 Trond Myklebust <trondmy@...il.com> wrote:
>
>> > That still leaves some open questions though...
>> >
>> > Is that enough to fix it? You'd still have the dirty pages lingering
>> > around, right? Would a umount -f presumably work at that point?
>>
>> 'umount -f' will kill any outstanding RPC calls that are causing the
>> mount to hang, but doesn't do anything to change page states or NFS
>> file/lock states.
>
> Should it though?
>
>        MNT_FORCE (since Linux 2.1.116)
>               Force  unmount  even  if busy.  This can cause data loss.  (Only
>               for NFS mounts.)
>
> Given that data loss is explicitly permitted, I suspect it should.
>
> Can we make MNT_FORCE on NFS not only abort outstanding RPC calls, but
> fail all subsequent RPC calls?  That might make it really useful.   You
> wouldn't even need to "kill -9" then.

Yes, but if the umount fails due to other conditions (for example an
application happens to still have a file open on that volume) then
that could leave you with a persistent messy situation on your hands.

Cheers
  Trond
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