Re: NFS causing oops when freeing namespace

[Oleg Nesterov]

On 01/17, Cedric Le Goater wrote:
>
> Oleg Nesterov wrote:
> > On 01/17, Daniel Hokka Zakrisson wrote:
> >> It was the only semi-plausible explanation I could come up with. I added a
> >> printk in do_exit right before exit_task_namespaces, where sighand was
> >> still set, and one right before the spin_lock_irq in lockd_down, where it
> >> had suddenly been set to NULL.
> > 
> > I can't reproduce the problem, but
> 
> I did on a 2.6.20-rc4-mm1.
> 
> >     do_exit:
> >             exit_notify(tsk);
> >             exit_task_namespaces(tsk);
> > 
> > the task could be reaped by its parent in between.
> 
> indeed. while it goes spleeping in lockd_down() just before it does
> 
>       spin_lock_irq(&current->sighand->siglock);
> 
> current->sighand is valid before interruptible_sleep_on_timeout() and
> not after.
>  
> > We should not use ->signal/->sighand after exit_notify().
> > 
> > Can we move exit_task_namespaces() up?
> 
> yes but I moved it down because it invalidates ->nsproxy ... 

Well, we can fix the symptom if we change lockd_down() to use
lock_task_sighand(), or something like this,

        --- NFS/fs/lockd/svc.c~lockd_down       2006-11-27 21:20:11.000000000 
+0300
        +++ NFS/fs/lockd/svc.c  2007-01-17 22:39:47.000000000 +0300
        @@ -314,6 +314,7 @@ void
         lockd_down(void)
         {
                static int warned;
        +       int sigpending;
         
                mutex_lock(&nlmsvc_mutex);
                if (nlmsvc_users) {
        @@ -334,16 +335,15 @@ lockd_down(void)
                 * Wait for the lockd process to exit, but since we're holding
                 * the lockd semaphore, we can't wait around forever ...
                 */
        -       clear_thread_flag(TIF_SIGPENDING);
        +       sigpending = test_and_clear_thread_flag(TIF_SIGPENDING);
                interruptible_sleep_on_timeout(&lockd_exit, HZ);
                if (nlmsvc_pid) {
                        printk(KERN_WARNING 
                                "lockd_down: lockd failed to exit, clearing 
pid\n");
                        nlmsvc_pid = 0;
                }
        -       spin_lock_irq(&current->sighand->siglock);
        -       recalc_sigpending();
        -       spin_unlock_irq(&current->sighand->siglock);
        +       if (sigpending) /* can be wrong at this point, harmless */
        +               set_thread_flag(TIF_SIGPENDING);
         out:
                mutex_unlock(&nlmsvc_mutex);
         }

but this is not good anyway.

Oleg.

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