[GIT pull] sched/urgent for v5.16-rc3

[Thomas Gleixner]

Linus,

please pull the latest sched/urgent branch from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-2021-11-28

up to:  dce1ca0525bf: sched/scs: Reset task stack state in bringup_cpu()


A single scheduler fix to ensure that there is no stale KASAN shadow state
left on the idle task's stack when a CPU is brought up after it was brought
down before.

Thanks,

	tglx

------------------>
Mark Rutland (1):
      sched/scs: Reset task stack state in bringup_cpu()


 kernel/cpu.c        | 7 +++++++
 kernel/sched/core.c | 4 ----
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 192e43a87407..407a2568f35e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -31,6 +31,7 @@
 #include <linux/smpboot.h>
 #include <linux/relay.h>
 #include <linux/slab.h>
+#include <linux/scs.h>
 #include <linux/percpu-rwsem.h>
 #include <linux/cpuset.h>
 
@@ -587,6 +588,12 @@ static int bringup_cpu(unsigned int cpu)
 	struct task_struct *idle = idle_thread_get(cpu);
 	int ret;
 
+	/*
+	 * Reset stale stack state from the last time this CPU was online.
+	 */
+	scs_task_reset(idle);
+	kasan_unpoison_task_stack(idle);
+
 	/*
 	 * Some architectures have to walk the irq descriptors to
 	 * setup the vector space for the cpu which comes online.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3c9b0fda64ac..76f9deeaa942 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8619,9 +8619,6 @@ void __init init_idle(struct task_struct *idle, int cpu)
 	idle->flags |= PF_IDLE | PF_KTHREAD | PF_NO_SETAFFINITY;
 	kthread_set_per_cpu(idle, cpu);
 
-	scs_task_reset(idle);
-	kasan_unpoison_task_stack(idle);
-
 #ifdef CONFIG_SMP
 	/*
 	 * It's possible that init_idle() gets called multiple times on a task,
@@ -8777,7 +8774,6 @@ 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 */
 }