The following commit has been merged into the sched/core branch of tip:
Commit-ID: d707faa64d03d26b529cc4aea59dab1b016d4d33
Gitweb: https://git.kernel.org/tip/d707faa64d03d26b529cc4aea59dab1b016d4d33
Author: Valentin Schneider <valentin.schneider@xxxxxxx>
AuthorDate: Fri, 13 Nov 2020 11:24:14
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 19 Nov 2020 11:25:45 +01:00
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@xxxxxxxxxx>
Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/8b62fd1ad1b18def27f18e2ee2df3ff5b36d0762.camel@xxxxxxxxxx
---
kernel/sched/core.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a6aaf9f..4d1fd4b 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.
|