linux-kernel - Re: [PATCH] lockd: convert reclaimer thread to kthread interface

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Message-Id: <1225802508.19864.2.camel@heimdal.trondhjem.org>
Date:	Tue, 04 Nov 2008 07:41:47 -0500
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	hch@...radead.org
Subject: Re: [PATCH] lockd: convert reclaimer thread to kthread interface

On Mon, 2008-11-03 at 19:19 -0500, Jeff Layton wrote:
> On Mon, 3 Nov 2008 13:12:15 -0800
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Wed, 29 Oct 2008 07:15:45 -0400
> > Jeff Layton <jlayton@...hat.com> wrote:
> > 
> > > My understanding is that there is a push to turn the kernel_thread
> > > interface into a non-exported symbol and move all kernel threads to use
> > > the kthread API. This patch changes lockd to use kthread_run to spawn
> > > the reclaimer thread.
> > > 
> > > I've made the assumption here that the extra module references taken
> > > when we spawn this thread are unnecessary and removed them. I've also
> > > added a KERN_ERR printk that pops if the thread can't be spawned to warn
> > > the admin that the locks won't be reclaimed.
> > > 
> > > I consider this patch 2.6.29 material.
> > > 
> > > Signed-off-by: Jeff Layton <jlayton@...hat.com>
> > > ---
> > >  fs/lockd/clntlock.c |   14 +++++++++-----
> > >  1 files changed, 9 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/fs/lockd/clntlock.c b/fs/lockd/clntlock.c
> > > index 8307dd6..fcc2378 100644
> > > --- a/fs/lockd/clntlock.c
> > > +++ b/fs/lockd/clntlock.c
> > > @@ -14,6 +14,7 @@
> > >  #include <linux/sunrpc/svc.h>
> > >  #include <linux/lockd/lockd.h>
> > >  #include <linux/smp_lock.h>
> > > +#include <linux/kthread.h>
> > >  
> > >  #define NLMDBG_FACILITY		NLMDBG_CLIENT
> > >  
> > > @@ -191,11 +192,15 @@ __be32 nlmclnt_grant(const struct sockaddr *addr, const struct nlm_lock *lock)
> > >  void
> > >  nlmclnt_recovery(struct nlm_host *host)
> > >  {
> > > +	struct task_struct *task;
> > > +
> > >  	if (!host->h_reclaiming++) {
> > >  		nlm_get_host(host);
> > > -		__module_get(THIS_MODULE);
> > > -		if (kernel_thread(reclaimer, host, CLONE_FS | CLONE_FILES) < 0)
> > > -			module_put(THIS_MODULE);
> > > +		task = kthread_run(reclaimer, host, "%s-reclaim", host->h_name);
> > > +		if (IS_ERR(task))
> > > +			printk(KERN_ERR "lockd: unable to spawn reclaimer "
> > > +				"thread. Locks for %s won't be reclaimed! "
> > > +				"(%ld)\n", host->h_name, PTR_ERR(task));
> > >  	}
> > >  }
> > >  
> > > @@ -207,7 +212,6 @@ reclaimer(void *ptr)
> > >  	struct file_lock *fl, *next;
> > >  	u32 nsmstate;
> > >  
> > > -	daemonize("%s-reclaim", host->h_name);
> > >  	allow_signal(SIGKILL);
> > >  
> > >  	down_write(&host->h_rwsem);
> > > @@ -261,5 +265,5 @@ restart:
> > >  	nlm_release_host(host);
> > >  	lockd_down();
> > >  	unlock_kernel();
> > > -	module_put_and_exit(0);
> > > +	return 0;
> > >  }
> > 
> > Looks OK to me.  I assume the SIGKILL handling has been carefully tested?
> > 
> > 
> > Is it correct to emit a warning and keep going if the thread didn't
> > start?  Or would it be safer&saner to fail the whole mount (or whatever
> > syscall we're doing here..)
> > 
> 
> Forgot to answer this part...
> 
> This thread gets kicked off when the server has rebooted and we need to
> reclaim our locks. There isn't a syscall on which we can return an
> error to the user.
> 
> Aside from just warning the admin, I'm not sure what we can do here. We
> might be able to start making all syscalls on the mount fail somehow,
> but I don't think we have infrastructure for that and that may be
> overkill anyway. I suppose we could also go to sleep and try to spawn the
> thread again, but there's no guarantee of success there.

We should consider implementing SIGLOST. That is the closest thing that
we have to a *NIX standard for signalling that remote filesystem state
has been lost.

Cheers
  Trond

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