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SubjectRe: [RFC] audit: avoid soft lockup in audit_log_start()
On Wed, 28 Aug 2013 18:54:36 -0400 Luiz Capitulino <lcapitulino@redhat.com> wrote:

> > Are you really sure that kauditd is stuck in schedule() and doesn't
> > come out?
>
> No, that's a guess. Inferred from:
>
> 1. I tried calling wake_up_interruptible(&kauditd_wait); right
> before wait_for_auditd(). Nothing changes
>
> 2. I added this debug printks:
>
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 91e53d0..27448ad 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -458,11 +458,14 @@ static int kauditd_thread(void *dummy)
> set_current_state(TASK_INTERRUPTIBLE);
> add_wait_queue(&kauditd_wait, &wait);
>
> + pr_emerg_ratelimited("*** sleeping\n");
> +
> if (!skb_queue_len(&audit_skb_queue)) {
> try_to_freeze();
> schedule();
> }
>
> + pr_emerg_ratelimited("*** waking up\n");
> __set_current_state(TASK_RUNNING);
> remove_wait_queue(&kauditd_wait, &wait);
> }
>
> I get several pairs of sleeping/waking up strings right before the
> system begins to shut down. Then it stops (even though we do
> have SKBs queued)

Well. I assume "*** sleeping" the last thing kauditd prints? If the
last print is "waking up" then obviously kauditd is stuck somewhere
else, which makes more sense. A sysrq-T (or echo t >
/proc/sysrq-trigger) should provide clues.

I'd remove the "_ratelimited" - you don't want your debug messages to be
ratelimited (ie: omitted).

> Now, the kauditd thread does exists when the soft lockup happens,
> I could verify that with crash.
>
> What's interesting is that I can only get it in that first reboot
> done by the firstboot script in RHEL6. I didn't manage to get it
> in any other way.
>
> I'm open to any debugging tips, but be gentle because I'm not
> very familiar with that stuff.


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