Oleg Nesterov wrote:
> 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(¤t->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(¤t->sighand->siglock);
> - recalc_sigpending();
> - spin_unlock_irq(¤t->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.
your first analysis was correct : exit_task_namespaces() should be moved
above exit_notify(tsk). It will require some extra fixes for nsproxy
though.
C.
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