From 89f19f04dc72363d912fd007a399cb10310eff6e Mon Sep 17 00:00:00 2001
From: Andrew Morton <akpm@linux-foundation.org>
Date: Sat, 19 Sep 2009 11:55:44 -0700
Subject: [PATCH] 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: 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>
---
include/linux/sched.h | 2 +-
kernel/sched.c | 10 ++--------
kernel/trace/trace.c | 8 +++++++-
3 files changed, 10 insertions(+), 10 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8af3d249170e0..cc37a3fa50659 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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;
diff --git a/kernel/sched.c b/kernel/sched.c
index faf4d463bbffb..575fb01390380 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -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);
}
/*
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index fd52a19dd1725..420232a1fbba0 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -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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