diff options
| author | Valentin Schneider <valentin.schneider@arm.com> | 2020-11-13 12:24:14 +0100 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2020-11-19 11:25:45 +0100 |
| commit | d707faa64d03d26b529cc4aea59dab1b016d4d33 (patch) | |
| tree | e8e55ee1de785f888d029134df4c1ac0d0dd7c66 /kernel/sched | |
| parent | sched/fair: Dissociate wakeup decisions from SD flag value (diff) | |
| download | linux-d707faa64d03d26b529cc4aea59dab1b016d4d33.tar.xz linux-d707faa64d03d26b529cc4aea59dab1b016d4d33.zip | |
sched/core: Add missing completion for affine_move_task() waiters
Qian reported that some fuzzer issuing sched_setaffinity() ends up stuck on
a wait_for_completion(). The problematic pattern seems to be:
affine_move_task()
// task_running() case
stop_one_cpu();
wait_for_completion(&pending->done);
Combined with, on the stopper side:
migration_cpu_stop()
// Task moved between unlocks and scheduling the stopper
task_rq(p) != rq &&
// task_running() case
dest_cpu >= 0
=> no complete_all()
This can happen with both PREEMPT and !PREEMPT, although !PREEMPT should
be more likely to see this given the targeted task has a much bigger window
to block and be woken up elsewhere before the stopper runs.
Make migration_cpu_stop() always look at pending affinity requests; signal
their completion if the stopper hits a rq mismatch but the task is
still within its allowed mask. When Migrate-Disable isn't involved, this
matches the previous set_cpus_allowed_ptr() vs migration_cpu_stop()
behaviour.
Fixes: 6d337eab041d ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()")
Reported-by: Qian Cai <cai@redhat.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/lkml/8b62fd1ad1b18def27f18e2ee2df3ff5b36d0762.camel@redhat.com
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/core.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a6aaf9fb3400..4d1fd4b783ee 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1923,7 +1923,7 @@ static int migration_cpu_stop(void *data) else p->wake_cpu = dest_cpu; - } else if (dest_cpu < 0) { + } else if (dest_cpu < 0 || pending) { /* * This happens when we get migrated between migrate_enable()'s * preempt_enable() and scheduling the stopper task. At that @@ -1934,6 +1934,17 @@ static int migration_cpu_stop(void *data) */ /* + * The task moved before the stopper got to run. We're holding + * ->pi_lock, so the allowed mask is stable - if it got + * somewhere allowed, we're done. + */ + if (pending && cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) { + p->migration_pending = NULL; + complete = true; + goto out; + } + + /* * When this was migrate_enable() but we no longer have an * @pending, a concurrent SCA 'fixed' things and we should be * valid again. Nothing to do. |