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Date: Sat, 5 Jul 2014 20:25:33 +0100 From: Russell King - ARM Linux <linux@....linux.org.uk> To: pawandeep oza <oza.contri.linux.kernel@...il.com> Cc: akpm@...ux-foundation.org, holt@....com, mingo@...nel.org, sboyd@...eaurora.org, k.khlebnikov@...sung.com, u.kleine-koenig@...gutronix.de, Nicolas Pitre <nicolas.pitre@...aro.org>, linux-arm-kernel@...ts.infradead.or, linux-kernel@...r.kernel.org 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())) return; 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 majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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