diff options
| author | Mike Galbraith <umgwanakikbuti@gmail.com> | 2016-02-17 04:02:59 +0100 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2016-02-27 14:28:49 +0000 |
| commit | 34bce1998711e65b8a7ef37eb92641cdc368587a (patch) | |
| tree | 239a217a5e90727d57dbcf6a428ea12a3d3a330f | |
| parent | feae3ca2e5e1a8f44aa6290255d3d9709985d0b2 (diff) | |
sched: fix __sched_setscheduler() vs load balancing race
__sched_setscheduler() may release rq->lock in pull_rt_task() as a task is
being changed rt -> fair class. load balancing may sneak in, move the task
behind __sched_setscheduler()'s back, which explodes in switched_to_fair()
when the passed but no longer valid rq is used. Tell can_migrate_task() to
say no if ->pi_lock is held.
@stable: Kernels that predate SCHED_DEADLINE can use this simple (and tested)
check in lieu of backport of the full 18 patch mainline treatment.
Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
[bwh: Backported to 3.2:
- Adjust numbering in the comment
- Adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Willy Tarreau <w@1wt.eu>
| -rw-r--r-- | kernel/sched_fair.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 4c6dae17cd1e..98e103988aad 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -2791,6 +2791,7 @@ int can_migrate_task(struct task_struct *p, struct rq *rq, int this_cpu, * 1) running (obviously), or * 2) cannot be migrated to this CPU due to cpus_allowed, or * 3) are cache-hot on their current CPU. + * 4) p->pi_lock is held. */ if (!cpumask_test_cpu(this_cpu, tsk_cpus_allowed(p))) { schedstat_inc(p, se.statistics.nr_failed_migrations_affine); @@ -2804,6 +2805,14 @@ int can_migrate_task(struct task_struct *p, struct rq *rq, int this_cpu, } /* + * rt -> fair class change may be in progress. If we sneak in should + * double_lock_balance() release rq->lock, and move the task, we will + * cause switched_to_fair() to meet a passed but no longer valid rq. + */ + if (raw_spin_is_locked(&p->pi_lock)) + return 0; + + /* * Aggressive migration if: * 1) task is cache cold, or * 2) too many balance attempts have failed. |