linux-kernel - [PATCH] cpu/hotplug: Fix rollback during error-out in takedown

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Message-Id: <1536042803-6152-1-git-send-email-neeraju@codeaurora.org>
Date:   Tue,  4 Sep 2018 12:03:23 +0530
From:   Neeraj Upadhyay <neeraju@...eaurora.org>
To:     tglx@...utronix.de, josh@...htriplett.org, peterz@...radead.org,
        mingo@...nel.org, jiangshanlai@...il.com, dzickus@...hat.com,
        brendan.jackman@....com, malat@...ian.org
Cc:     linux-kernel@...r.kernel.org, sramana@...eaurora.org,
        linux-arm-msm@...r.kernel.org,
        Neeraj Upadhyay <neeraju@...eaurora.org>
Subject: [PATCH] cpu/hotplug: Fix rollback during error-out in takedown_cpu()

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@...eaurora.org>
---
 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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