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sched/fair: Fix detection of per-CPU kthreads waking a task

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[ 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: 52262ee567 ("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>
This commit is contained in:
Vincent Donnefort 2021-12-01 14:34:50 +00:00 committed by Greg Kroah-Hartman
parent ec121517ac
commit d7d5b3bc52
1 changed files with 1 additions and 0 deletions
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kernel/sched/fair.c
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@ -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;