Commit 89f19f04 authored by Andrew Morton's avatar Andrew Morton Committed by Ingo Molnar
Browse files

sched: Fix raciness in runqueue_is_locked() 



runqueue_is_locked() is unavoidably racy due to a poor interface design.
It does

	cpu = get_cpu()
	ret = some_perpcu_thing(cpu);
	put_cpu(cpu);
	return ret;

Its return value is unreliable.

Fix.

Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <200909191855.n8JItiko022148@imap1.linux-foundation.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 3f04e8cd

include/linux/sched.h

+1 −1
Original line number Diff line number Diff line
@@ -257,7 +257,7 @@ extern asmlinkage void schedule_tail(struct task_struct *prev); 
extern void init_idle(struct task_struct *idle, int cpu);

extern void init_idle_bootup_task(struct task_struct *idle);



extern int runqueue_is_locked(void);

extern int runqueue_is_locked(int cpu);

extern void task_rq_unlock_wait(struct task_struct *p);



extern cpumask_var_t nohz_cpu_mask;

kernel/sched.c

+2 −8
Original line number Diff line number Diff line
@@ -681,15 +681,9 @@ inline void update_rq_clock(struct rq *rq) 
 * This interface allows printk to be called with the runqueue lock

 * held and know whether or not it is OK to wake up the klogd.

 */

int runqueue_is_locked(void)

int runqueue_is_locked(int cpu)

{

	int cpu = get_cpu();

	struct rq *rq = cpu_rq(cpu);

	int ret;



	ret = spin_is_locked(&rq->lock);

	put_cpu();

	return ret;

	return spin_is_locked(&cpu_rq(cpu)->lock);

}



/*

kernel/trace/trace.c

+7 −1
Original line number Diff line number Diff line
@@ -275,12 +275,18 @@ static DEFINE_SPINLOCK(tracing_start_lock); 
 */

void trace_wake_up(void)

{

	int cpu;



	if (trace_flags & TRACE_ITER_BLOCK)

		return;

	/*

	 * The runqueue_is_locked() can fail, but this is the best we

	 * have for now:

	 */

	if (!(trace_flags & TRACE_ITER_BLOCK) && !runqueue_is_locked())

	cpu = get_cpu();

	if (!runqueue_is_locked(cpu))

		wake_up(&trace_wait);

	put_cpu();

}



static int __init set_buf_size(char *str)

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