[tip: sched/urgent] sched/scs: Reset the shadow stack when idle_task_exit

[tip-bot2 for Woody Lin]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     63acd42c0d4942f74710b11c38602fb14dea7320
Gitweb:        https://git.kernel.org/tip/63acd42c0d4942f74710b11c38602fb14dea7320
Author:        Woody Lin <woodylin@xxxxxxxxxx>
AuthorDate:    Tue, 12 Oct 2021 16:35:21 +08:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 19 Oct 2021 17:46:11 +02:00

sched/scs: Reset the shadow stack when idle_task_exit

Commit f1a0a376ca0c ("sched/core: Initialize the idle task with
preemption disabled") removed the init_idle() call from
idle_thread_get(). This was the sole call-path on hotplug that resets
the Shadow Call Stack (scs) Stack Pointer (sp).

Not resetting the scs-sp leads to scs overflow after enough hotplug
cycles. Therefore add an explicit scs_task_reset() to the hotplug code
to make sure the scs-sp does get reset on hotplug.

Fixes: f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled")
Signed-off-by: Woody Lin <woodylin@xxxxxxxxxx>
[peterz: Changelog]
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Link: https://lore.kernel.org/r/20211012083521.973587-1-woodylin@xxxxxxxxxx
---
 kernel/sched/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1bba412..f21714e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8795,6 +8795,7 @@ void idle_task_exit(void)
 		finish_arch_post_lock_switch();
 	}
 
+	scs_task_reset(current);
 	/* finish_cpu(), as ran on the BP, will clean up the active_mm state */
 }