3.2.78-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Mike Galbraith <umgwanakikbuti@xxxxxxxxx> __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sneak in, move the task behind __sched_setscheduler()'s back, which explodes in switched_to_fair() when the passed but no longer valid rq is used.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@xxxxxxxxx> [bwh: Backported to 3.2: - Adjust numbering in the comment - Adjust filename] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> Cc: Byungchul Park <byungchul.park@xxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Willy Tarreau <w@xxxxxx> --- kernel/sched/fair.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -2791,6 +2791,7 @@ int can_migrate_task(struct task_struct * 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 } /* + * 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lock, and move the task, we will + * cause switched_to_fair() to meet a passed but no longer valid rq.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. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html