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    SubjectRe: [PATCH] lockd: convert reclaimer thread to kthread interface
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    On Mon, 2008-11-03 at 19:19 -0500, Jeff Layton wrote:
    > On Mon, 3 Nov 2008 13:12:15 -0800
    > Andrew Morton <akpm@linux-foundation.org> wrote:
    >
    > > On Wed, 29 Oct 2008 07:15:45 -0400
    > > Jeff Layton <jlayton@redhat.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@redhat.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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