sched/scs: Reset the shadow stack when idle_task_exit

stable inclusion
from stable-5.10.76
commit 96fe5061291d9e9734abf6bb187ef7532824522d
bugzilla: 182988 https://gitee.com/openeuler/kernel/issues/I4IAHF

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=96fe5061291d9e9734abf6bb187ef7532824522d



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[ Upstream commit 63acd42c ]

Commit f1a0a376 ("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: f1a0a376 ("sched/core: Initialize the idle task with preemption disabled")
Signed-off-by: Woody Lin <woodylin@google.com>
[peterz: Changelog]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lore.kernel.org/r/20211012083521.973587-1-woodylin@google.com


Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>

Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>