linux-kernel - [PATCH 1/2] stop_machine: Use non-atomic read multi_stop

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Date:   Fri, 20 Oct 2023 22:43:33 +0800
From:   Rong Tao <rtoax@...mail.com>
To:     mark.rutland@....com, elver@...gle.com,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        rongtao@...tc.cn, rtoax@...mail.com, tglx@...utronix.de
Subject: [PATCH 1/2] stop_machine: Use non-atomic read multi_stop_data::state clearly

From: Rong Tao <rongtao@...tc.cn>

commit b1fc58333575 ("stop_machine: Avoid potential race behaviour")
solved the race behaviour problem, to better show that race behaviour
does not exist, pass the 'curstate' directly to ack_state() instead of
refetching msdata->state in ack_state().

Signed-off-by: Rong Tao <rongtao@...tc.cn>
---
 kernel/stop_machine.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index cedb17ba158a..268c2e581698 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -188,10 +188,11 @@ static void set_state(struct multi_stop_data *msdata,
 }
 
 /* Last one to ack a state moves to the next state. */
-static void ack_state(struct multi_stop_data *msdata)
+static void ack_state(struct multi_stop_data *msdata,
+		      enum multi_stop_state curstate)
 {
 	if (atomic_dec_and_test(&msdata->thread_ack))
-		set_state(msdata, msdata->state + 1);
+		set_state(msdata, curstate + 1);
 }
 
 notrace void __weak stop_machine_yield(const struct cpumask *cpumask)
@@ -242,7 +243,7 @@ static int multi_cpu_stop(void *data)
 			default:
 				break;
 			}
-			ack_state(msdata);
+			ack_state(msdata, curstate);
 		} else if (curstate > MULTI_STOP_PREPARE) {
 			/*
 			 * At this stage all other CPUs we depend on must spin
-- 
2.41.0