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[PATCH] sched: CPU hotplug race vs. set_cpus_allowed() 

There is a race between set_cpus_allowed() and move_task_off_dead_cpu().
__migrate_task() doesn't report any err code, so task can be left on its
runqueue if its cpus_allowed mask changed so that dest_cpu is not longer a
possible target.  Also, chaning cpus_allowed mask requires rq->lock being
held.

Signed-off-by: Kirill Korotaev <dev@openvz.org>
Acked-By: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Kirill Korotaev 2006-06-27 02:54:32 -07:00 committed by Linus Torvalds
parent cc94abfcbc
commit efc30814a8
1 changed files with 14 additions and 4 deletions
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18
kernel/sched.c
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@ -4412,13 +4412,16 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed);
*
* So we race with normal scheduler movements, but that's OK, as long
* as the task is no longer on this CPU.
*
* Returns non-zero if task was successfully migrated.
*/
static void __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
{
runqueue_t *rq_dest, *rq_src;
int ret = 0;
if (unlikely(cpu_is_offline(dest_cpu)))
return;
return ret;
rq_src = cpu_rq(src_cpu);
rq_dest = cpu_rq(dest_cpu);
@ -4446,9 +4449,10 @@ static void __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
if (TASK_PREEMPTS_CURR(p, rq_dest))
resched_task(rq_dest->curr);
}
ret = 1;
out:
double_rq_unlock(rq_src, rq_dest);
return ret;
}
/*
@ -4518,9 +4522,12 @@ wait_to_die:
/* Figure out where task on dead CPU should go, use force if neccessary. */
static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *tsk)
{
runqueue_t *rq;
unsigned long flags;
int dest_cpu;
cpumask_t mask;
restart:
/* On same node? */
mask = node_to_cpumask(cpu_to_node(dead_cpu));
cpus_and(mask, mask, tsk->cpus_allowed);
@ -4532,8 +4539,10 @@ static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *tsk)
/* No more Mr. Nice Guy. */
if (dest_cpu == NR_CPUS) {
rq = task_rq_lock(tsk, &flags);
cpus_setall(tsk->cpus_allowed);
dest_cpu = any_online_cpu(tsk->cpus_allowed);
task_rq_unlock(rq, &flags);
/*
* Don't tell them about moving exiting tasks or
@ -4545,7 +4554,8 @@ static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *tsk)
"longer affine to cpu%d\n",
tsk->pid, tsk->comm, dead_cpu);
}
__migrate_task(tsk, dead_cpu, dest_cpu);
if (!__migrate_task(tsk, dead_cpu, dest_cpu))
goto restart;
}
/*