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sched: Fix affine_move_task() self-concurrency

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Consider:

   sched_setaffinity(p, X);		sched_setaffinity(p, Y);

Then the first will install p->migration_pending = &my_pending; and
issue stop_one_cpu_nowait(pending); and the second one will read
p->migration_pending and _also_ issue: stop_one_cpu_nowait(pending),
the _SAME_ @pending.

This causes stopper list corruption.

Add set_affinity_pending::stop_pending, to indicate if a stopper is in
progress.

Fixes: 6d337eab04 ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()")
Cc: stable@kernel.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210224131355.649146419@infradead.org
This commit is contained in:
Peter Zijlstra 2021-02-24 11:31:09 +01:00 committed by Ingo Molnar
parent 3f1bc119cd
commit 9e81889c76
1 changed files with 12 additions and 3 deletions
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15
kernel/sched/core.c
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@ -1864,6 +1864,7 @@ struct migration_arg {
struct set_affinity_pending {
refcount_t refs;
unsigned int stop_pending;
struct completion done;
struct cpu_stop_work stop_work;
struct migration_arg arg;
@ -1982,12 +1983,15 @@ static int migration_cpu_stop(void *data)
* determine is_migration_disabled() and so have to chase after
* it.
*/
WARN_ON_ONCE(!pending->stop_pending);
task_rq_unlock(rq, p, &rf);
stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,
&pending->arg, &pending->stop_work);
return 0;
}
out:
if (pending)
pending->stop_pending = false;
task_rq_unlock(rq, p, &rf);
if (complete)
@ -2183,7 +2187,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
int dest_cpu, unsigned int flags)
{
struct set_affinity_pending my_pending = { }, *pending = NULL;
bool complete = false;
bool stop_pending, complete = false;
/* Can the task run on the task's current CPU? If so, we're done */
if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) {
@ -2256,14 +2260,19 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
* anything else we cannot do is_migration_disabled(), punt
* and have the stopper function handle it all race-free.
*/
stop_pending = pending->stop_pending;
if (!stop_pending)
pending->stop_pending = true;
refcount_inc(&pending->refs); /* pending->{arg,stop_work} */
if (flags & SCA_MIGRATE_ENABLE)
p->migration_flags &= ~MDF_PUSH;
task_rq_unlock(rq, p, rf);
stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
&pending->arg, &pending->stop_work);
if (!stop_pending) {
stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
&pending->arg, &pending->stop_work);
}
if (flags & SCA_MIGRATE_ENABLE)
return 0;