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Commit c3485dd4 authored by Pavankumar Kondeti's avatar Pavankumar Kondeti Committed by Gerrit - the friendly Code Review server
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sched/cputime: fix a deadlock on 32bit systems 



cpu_hardirq_time and cpu_softirq_time are protected with
seqlock on 32bit systems. There is a potential deadlock
with this seqlock and rq->lock.

CPU 1                             CPU0
==========================        ========================
--> acquire CPU0 rq->lock         --> __irq_enter()
----> task enqueue/dequeue        ----> irqtime_account_irq()
------> update_rq_clock()         ------> irq_time_write_begin()
--------> irq_time_read()         --------> sched_account_irqtime()
(waiting for the seqlock          (waiting for the CPU0 rq->lock)
held in irq_time_write_begin()

Fix this issue by dropping the seqlock before calling
sched_account_irqtime()

Change-Id: I29a33876e372f99435a57cc11eada9c8cfd59a3f
Signed-off-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
parent 1cba7830

kernel/sched/cputime.c

+9 −6
Original line number Diff line number Diff line
@@ -51,6 +51,7 @@ void irqtime_account_irq(struct task_struct *curr) 
	s64 delta;

	int cpu;

	u64 wallclock;

	bool account = true;



	if (!sched_clock_irqtime)

		return;
@@ -69,16 +70,18 @@ void irqtime_account_irq(struct task_struct *curr) 
	 * in that case, so as not to confuse scheduler with a special task

	 * that do not consume any time, but still wants to run.

	 */

	if (hardirq_count()) {

	if (hardirq_count())

		__this_cpu_add(cpu_hardirq_time, delta);

		sched_account_irqtime(cpu, curr, delta, wallclock);

	} else if (in_serving_softirq() && curr != this_cpu_ksoftirqd()) {

	else if (in_serving_softirq() && curr != this_cpu_ksoftirqd())

		__this_cpu_add(cpu_softirq_time, delta);

		sched_account_irqtime(cpu, curr, delta, wallclock);

	}



	else

		account = false;



	irq_time_write_end();



	if (account)

		sched_account_irqtime(cpu, curr, delta, wallclock);



	local_irq_restore(flags);

}

EXPORT_SYMBOL_GPL(irqtime_account_irq);