linux-kernel - Re: [PATCH] Switch nfs/callback.c to using struct pid, not pid

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Message-Id: <1188396641.6580.62.camel@heimdal.trondhjem.org>
Date:	Wed, 29 Aug 2007 10:10:41 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Pavel Emelyanov <xemul@...nvz.org>, Andrew Morton <akpm@...l.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Sukadev Bhattiprolu <sukadev@...ibm.com>,
	Linux Containers <containers@...ts.osdl.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Switch nfs/callback.c to using struct pid, not pid_t

On Wed, 2007-08-29 at 14:52 +0100, Christoph Hellwig wrote:
> On Wed, Aug 29, 2007 at 05:36:24PM +0400, Pavel Emelyanov wrote:
> > Pid namespaces make it dangerous to use pid and tgid values
> > when run in some namespace. The struct pid itself is going
> > to be the only way for working with task pids, so make the
> > nfs callback thread use it.
> > 
> > Since nfs_callback_info.pid is set to current's one and reset
> > on the thread exit, it is safe not to get the struct pid. 
> > 
> > Since this pid is used later under lock_kernel() w/o sleeping 
> > operations, checking for i to be not NULL and killing the 
> > thread with kill_pid() is safe.
> 
> NACK.  This just makes the code even more obscure.  Please get rid
> of the pid references entirely and convert the code to the kthread
> API.

That would require converting the full sunrpc server code to use
kthreads, which again means changing nfsd, and lockd too.

I'm not saying that is a bad thing, but it is nontrivial to do. In
particular, kthread's abominable shutdown mechanism simply does not work
or scale when the thread is listening for new requests in svc_recv().

Cheers
  Trond

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