lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [day] [month] [year] [list]
Date:	Sat, 5 Jul 2014 20:25:33 +0100
From:	Russell King - ARM Linux <>
To:	pawandeep oza <>
	Nicolas Pitre <>,
Subject: Re: [PATCH] machine_power_off: not only local_irq_disable but also
	do disable preemption

On Sun, Jul 06, 2014 at 12:20:03AM +0530, pawandeep oza wrote:
> preempt_check_resched would check TIF_NEED_RESCHED
> #define preempt_check_resched() \
> do { \
> if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
> preempt_schedule(); \
> } while (0)
> there is a chance that just beofre we disabled irqs, somebody would have
> marked the flag to current, and
> later on, it might happen that, current gets replaced by the process which
> tries to hold a spin_lock which has already been previosuly held by CPU1
> when
> was being plugged out by smp_send_stop.

And preempt_schedule() contains:

         * If there is a non-zero preempt_count or interrupts are disabled,
         * we do not want to preempt the current task. Just return..
        if (likely(!preemptible()))

where preemptible() is defined as:

	(preempt_count() == 0 && !irqs_disabled())

which means... if interrupts are disabled (as they are) we don't
return from preempt_schedule() without doing anything.

Scheduling with interrupts disabled is a bug.  If you need to add
preempt_disable() before local_irq_disable() to prevent it, then
there's a bug somewhere else, and we don't "fix" that by adding
preempt_disable().  The real bug needs to be found and fixed.

FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists