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sched: avoid stack var in move_task_off_dead_cpu, fix

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Impact: locking fix

We can't call cpuset_cpus_allowed_locked() with the rq lock held.
However, the rq lock merely protects us from (1) cpu_online_mask changing
and (2) someone else changing p->cpus_allowed.

The first can't happen because we're being called from a cpu hotplug
notifier.  The second doesn't really matter: we are forcing the task off
a CPU it was affine to, so we're not doing very well anyway.

So we remove the rq lock from this path, and all is good.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Rusty Russell
2008-11-25 09:59:20 +10:30
committed by Ingo Molnar
parent 3d8cbdf865
commit 1224e376f2
1 changed files with 0 additions and 4 deletions
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4
kernel/sched.c
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@@ -6126,8 +6126,6 @@ static int __migrate_task_irq(struct task_struct *p, int src_cpu, int dest_cpu)
*/ */
static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p) static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p)
{ {
unsigned long flags;
struct rq *rq;
int dest_cpu; int dest_cpu;
/* FIXME: Use cpumask_of_node here. */ /* FIXME: Use cpumask_of_node here. */
cpumask_t _nodemask = node_to_cpumask(cpu_to_node(dead_cpu)); cpumask_t _nodemask = node_to_cpumask(cpu_to_node(dead_cpu));
@@ -6146,10 +6144,8 @@ again:
/* No more Mr. Nice Guy. */ /* No more Mr. Nice Guy. */
if (dest_cpu >= nr_cpu_ids) { if (dest_cpu >= nr_cpu_ids) {
rq = task_rq_lock(p, &flags);
cpuset_cpus_allowed_locked(p, &p->cpus_allowed); cpuset_cpus_allowed_locked(p, &p->cpus_allowed);
dest_cpu = cpumask_any_and(cpu_online_mask, &p->cpus_allowed); dest_cpu = cpumask_any_and(cpu_online_mask, &p->cpus_allowed);
task_rq_unlock(rq, &flags);
/* /*
* Don't tell them about moving exiting tasks or * Don't tell them about moving exiting tasks or