From: Vincent Donnefort vincent.donnefort@arm.com
[ Upstream commit 8b4e74ccb582797f6f0b0a50372ebd9fd2372a27 ]
select_idle_sibling() has a special case for tasks woken up by a per-CPU kthread, where the selected CPU is the previous one. However, the current condition for this exit path is incomplete. A task can wake up from an interrupt context (e.g. hrtimer), while a per-CPU kthread is running. A such scenario would spuriously trigger the special case described above. Also, a recent change made the idle task like a regular per-CPU kthread, hence making that situation more likely to happen (is_per_cpu_kthread(swapper) being true now).
Checking for task context makes sure select_idle_sibling() will not interpret a wake up from any other context as a wake up by a per-CPU kthread.
Fixes: 52262ee567ad ("sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression") Signed-off-by: Vincent Donnefort vincent.donnefort@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Vincent Guittot vincent.guittot@linaro.org Reviewed-by: Valentin Schneider valentin.schneider@arm.com Link: https://lore.kernel.org/r/20211201143450.479472-1-vincent.donnefort@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/fair.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c004e3b89c324..a7589552be5fc 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6284,6 +6284,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) * pattern is IO completions. */ if (is_per_cpu_kthread(current) && + in_task() && prev == smp_processor_id() && this_rq()->nr_running <= 1) { return prev;