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

[Trond Myklebust]

On Nov 3, 2008, at 19:19, Jeff Layton <jlayton@xxxxxxxxxx> wrote:

> On Mon, 3 Nov 2008 13:12:15 -0800
> Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> > On Wed, 29 Oct 2008 07:15:45 -0400
> > Jeff Layton <jlayton@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > ---
> > > 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.
> >

At some point RSN we should implement SIGLOST. That would be the  
closest thing we have to a *NIX standard for reporting the loss of  
filesystem state to the application.

Trond
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