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sched: Fix raciness in runqueue_is_locked()

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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: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <200909191855.n8JItiko022148@imap1.linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Andrew Morton 2009-09-19 11:55:44 -07:00 committed by Ingo Molnar
parent 3f04e8cd5b
commit 89f19f04dc
3 changed files with 10 additions and 10 deletions
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2
include/linux/sched.h
View file

@ -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;

10
kernel/sched.c
View file

@ -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);
}
/*

8
kernel/trace/trace.c
View file

@ -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)