linux-kernel - Re: [2.6.30-rc1] RCU detected CPU 1 stall

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Date:	Fri, 10 Apr 2009 16:03:53 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-kernel@...r.kernel.org, hugh@...itas.com, jmorris@...ei.org,
	akpm@...ux-foundation.org
Subject: Re: [2.6.30-rc1] RCU detected CPU 1 stall

On Fri, Apr 10, 2009 at 07:22:03AM -0700, Paul E. McKenney wrote:

> Hmmmm...  This indicates that CPU 1 was spinning in the kernel for
> a long time.  At 250 HZ, 32,565 jiffies is 130 seconds, or just over
> two -minutes-.  Ouch!!!
> 
> The interrupt happened on the stalled CPU, so we know that interrupts
> were enabled.  Because we have CONFIG_PREEMPT_NONE=y, there is no
> preemption, so preemption need not be disabled.  This could be due
> to lock contention, or even a simple infinite loop.
> 
> The timer interrupt (apic_timer_interrupt) occurred in either
> __bprm_mm_init(), __get_user_4(), count(), or do_execve().  There
> have been some recent changes around check_unsafe_exec() -- any
> possibility that these introduced excessive lock contention or
> an infinite loop?  Ditto for the recent security fixes?

Oh, joy... the loop in there is this:
        for (t = next_thread(p); t != p; t = next_thread(t)) {
                if (t->fs == p->fs)
                        n_fs++;
        }
I find it hard to believe that it can take two minutes, though.
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