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SubjectRe: NFS causing oops when freeing namespace
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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