[PATCH] cpu/hotplug: Fix rollback during error-out in takedown_cpu()

[Neeraj Upadhyay]

If takedown_cpu() fails during _cpu_down(), st->state is reset,
by calling cpuhp_reset_state(). This results in an additional
increment of st->state, which results in CPUHP_AP_SMPBOOT_THREADS
state being skipped during rollback. Fix this by not calling
cpuhp_reset_state() and doing the state reset directly in
_cpu_down().

Fixes: 4dddfb5faa61 ("smp/hotplug: Rewrite AP state machine core")
Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
---
 kernel/cpu.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index aa7fe85..9f49edb 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -970,7 +970,14 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
 	 */
 	ret = cpuhp_down_callbacks(cpu, st, target);
 	if (ret && st->state > CPUHP_TEARDOWN_CPU && st->state < prev_state) {
-		cpuhp_reset_state(st, prev_state);
+		/*
+		 * As st->last is not set, cpuhp_reset_state() increments
+		 * st->state, which results in CPUHP_AP_SMPBOOT_THREADS being
+		 * skipped during rollback. So, don't use it here.
+		 */
+		st->rollback = true;
+		st->target = prev_state;
+		st->bringup = !st->bringup;
 		__cpuhp_kick_ap(st);
 	}
 
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