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Date: Mon, 9 Sep 2013 10:54:43 -0400
From: Luiz Capitulino <lcapitulino@redhat.com>
To: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: linux-kernel@vger.kernel.org, oleg@redhat.com, eparis@redhat.com,
        akpm@linux-foundation.org, rgb@redhat.com
Subject: Re: [RFC] audit: avoid soft lockup in audit_log_start()
Message-ID: <20130909105443.72e525cb@redhat.com>
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On Mon, 09 Sep 2013 18:32:13 +0400
Konstantin Khlebnikov <khlebnikov@openvz.org> wrote:

> Luiz Capitulino wrote:
> > I'm getting the following soft lockup:
> >
> > CPU: 6 PID: 2278 Comm: killall5 Tainted: GF            3.11.0-rc7+ #1
> > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> >   0000000000000099 ffff88011fd83de8 ffffffff815324df 0000000000002800
> >   ffffffff817d48f9 ffff88011fd83e68 ffffffff8152e669 ffff88011fd83e68
> >   ffffffff00000008 ffff88011fd83e78 ffff88011fd83e18 0000004081dac040
> > Call Trace:
> >   <IRQ>   [<ffffffff815324df>] dump_stack+0x46/0x58
> >   [<ffffffff8152e669>] panic+0xbb/0x1c4
> >   [<ffffffff810d03c3>] watchdog_timer_fn+0x163/0x170
> >   [<ffffffff8106c691>] __run_hrtimer+0x81/0x1c0
> >   [<ffffffff810d0260>] ? watchdog+0x30/0x30
> >   [<ffffffff8106cea7>] hrtimer_interrupt+0x107/0x240
> >   [<ffffffff8102f61b>] local_apic_timer_interrupt+0x3b/0x60
> >   [<ffffffff81542465>] smp_apic_timer_interrupt+0x45/0x60
> >   [<ffffffff8154124a>] apic_timer_interrupt+0x6a/0x70
> >   <EOI>   [<ffffffff810c2f5f>] ? audit_log_start+0xbf/0x430
> >   [<ffffffff810c2fe7>] ? audit_log_start+0x147/0x430
> >   [<ffffffff81079030>] ? try_to_wake_up+0x2a0/0x2a0
> >   [<ffffffff810c86be>] audit_log_exit+0x6ae/0xc30
> >   [<ffffffff81188662>] ? __alloc_fd+0x42/0x100
> >   [<ffffffff810c98e7>] __audit_syscall_exit+0x257/0x2b0
> >   [<ffffffff81540794>] sysret_audit+0x17/0x21
> >
> > The reproducer is somewhat unusual:
> >
> >   1. Install RHEL6.5 (maybe a similar older user-space will do)
> >   2. Boot the just installed system
> >   3. In this first boot you'll meet the firstboot script, which
> >      will do some setup and (depending on your answers) it will
> >      reboot the machine
> >   4. During that first reboot the system hangs while terminating
> >      all processes:
> >
> >         Sending all processes the TERM signal...
> >
> >      It's when the soft lockup above happens. And yes, I managed
> >      to get this with latest upstream kernel (HEAD fa8218def1b1)
> >
> > I'm reproducing it on a VM, but the first report was on bare-metal.
> >
> > This is what is happening:
> >
> >   1. audit_log_start() is called
> >   2. As we have SKBs waiting in audit_skb_queue and all conditions
> >      evaluate to true, we sleep in wait_for_auditd()
> >   3. Go to 2, until sleep_time gets negative and audit_log_start()
> >      just busy-waits
> >
> > Now, *why* this is happening is a mistery to me. I tried debugging
> > it, but all I could find is that at some point the kauditd thread
> > never wakes up after having called schedule(). I even tried waking
> > it up before calling wait_for_auditd(), but it didn't.
> 
> We run into the same problem in rhel6 kernel.
> 
> "readahead-collector" uses audit interface and sometimes stuck in 'stopped' state.

Yes, please also see:

 http://marc.info/?l=linux-kernel&m=137818375024600&w=2

> After commit 829199197a430dade2519d54f5545c4a094393b8
> (which was backported by RH into their kernel)
> audit emiters will block forever if userspace daemon cannot handle backlog.
> That commit just breaks timeout condition, after timeout waiting loop turns
> into busy loop until deamon dies or returns back to work.
> 
> this trivial patch should fix that problem
> 
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1215,9 +1215,10 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
> 
>                          sleep_time = timeout_start + audit_backlog_wait_time -
>                                          jiffies;
> -                       if ((long)sleep_time > 0)
> +                       if ((long)sleep_time > 0) {
>                                  wait_for_auditd(sleep_time);
> -                       continue;
> +                               continue;
> +                       }
>                  }


Chuck Anderson posted a similar fix:

 http://marc.info/?l=linux-kernel&m=137817994623832&w=2

I still get a hang for around a minute with Chuck's fix, I believe I'll
get the same thing with yours.
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