The patch titled
sched: CPU hotplug race vs. set_cpus_allowed()
has been added to the -mm tree. Its filename is
sched-cpu-hotplug-race-vs-set_cpus_allowed.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: sched: CPU hotplug race vs. set_cpus_allowed()
From: Kirill Korotaev <dev@xxxxx>
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@xxxxxxxxxx>
Acked-By: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
kernel/sched.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff -puN kernel/sched.c~sched-cpu-hotplug-race-vs-set_cpus_allowed kernel/sched.c
--- a/kernel/sched.c~sched-cpu-hotplug-race-vs-set_cpus_allowed
+++ a/kernel/sched.c
@@ -4443,13 +4443,16 @@ 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);
@@ -4477,9 +4480,10 @@ static void __migrate_task(struct task_s
if (TASK_PREEMPTS_CURR(p, rq_dest))
resched_task(rq_dest->curr);
}
-
+ ret = 1;
out:
double_rq_unlock(rq_src, rq_dest);
+ return ret;
}
/*
@@ -4549,9 +4553,12 @@ 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);
@@ -4563,8 +4570,10 @@ static void move_task_off_dead_cpu(int d
/* 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
@@ -4576,7 +4585,8 @@ static void move_task_off_dead_cpu(int d
"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;
}
/*
_
Patches currently in -mm which might be from dev@xxxxx are
sched-cpu-hotplug-race-vs-set_cpus_allowed.patch
ipc-namespace-utils-compilation-fix.patch
-
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