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Subject: Re: [ANNOUNCE] 3.0.4-rt13
From: Peter Zijlstra <peterz@infradead.org>
To: Mike Galbraith <efault@gmx.de>
Cc: Thomas Gleixner <tglx@linutronix.de>, LKML <linux-kernel@vger.kernel.org>,
        linux-rt-users <linux-rt-users@vger.kernel.org>
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Date: Mon, 12 Sep 2011 10:59:08 +0200
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On Sun, 2011-09-11 at 12:35 +0200, Mike Galbraith wrote:
> (gdb) list *do_sigtimedwait+0x62
> 0xffffffff8104f3e2 is in do_sigtimedwait (kernel/signal.c:2628).
> 2623             * Invert the set of allowed signals to get those we want to block.
> 2624             */
> 2625            sigdelsetmask(&mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
> 2626            signotset(&mask);
> 2627
> 2628            spin_lock_irq(&tsk->sighand->siglock);
> 2629            sig = dequeue_signal(tsk, &mask, info);
> 2630            if (!sig && timeout) {
> 2631                    /*
> 2632                     * None ready, temporarily unblock those we're interested
> (gdb) list *do_sigtimedwait+0x15f
> 0xffffffff8104f4df is in do_sigtimedwait (kernel/signal.c:2642).
> 2637                    tsk->real_blocked = tsk->blocked;
> 2638                    sigandsets(&tsk->blocked, &tsk->blocked, &mask);
> 2639                    recalc_sigpending();
> 2640                    spin_unlock_irq(&tsk->sighand->siglock);
> 2641
> 2642                    timeout = schedule_timeout_interruptible(timeout);
> 2643
> 2644                    spin_lock_irq(&tsk->sighand->siglock);
> 2645                    __set_task_blocked(tsk, &tsk->real_blocked);
> 2646                    siginitset(&tsk->real_blocked, 0);
> 


Right, so what Thomas says.. Now admittedly I haven't had my morning
juice yet, but staring at that function I can't see why that warning
would trigger at all.

I'm going to try and reproduce, but Thomas is already saying he can't,
so I'm not too confident.

I you can easily trigger this, could you add some trace_printk() to
migrate_disable/enable that prints both counters etc.. so we can see wtf
happens?