Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

589f1222 · Linus Torvalds <[email protected]> · 2019-10-20 06:22:25 -04:00

Pull stop-machine fix from Thomas Gleixner:
 "A single fix, amending stop machine with WRITE/READ_ONCE() to address
  the fallout of KCSAN"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  stop_machine: Avoid potential race behaviour

Commit: 589f1222e043ab1f5cbce558cfaed0c0fa76e7bb
Parents: 531e93d1 · b1fc5833

Merge commit. Changes below are compared with the first parent: 531e93d1.

Changes

1 files changed · +6 −4

File	Status	Add	Del	Content
kernel/stop_machine.c	modified	+6	−4	View file

kernel/stop_machine.c

View file

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index c7031a2..998d50e 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -7,6 +7,7 @@
  * Copyright (C) 2010		SUSE Linux Products GmbH
  * Copyright (C) 2010		Tejun Heo <[email protected]>
  */
+#include <linux/compiler.h>
 #include <linux/completion.h>
 #include <linux/cpu.h>
 #include <linux/init.h>
@@ -167,7 +168,7 @@ static void set_state(struct multi_stop_data *msdata,
 	/* Reset ack counter. */
 	atomic_set(&msdata->thread_ack, msdata->num_threads);
 	smp_wmb();
-	msdata->state = newstate;
+	WRITE_ONCE(msdata->state, newstate);
 }
 
 /* Last one to ack a state moves to the next state. */
@@ -186,7 +187,7 @@ void __weak stop_machine_yield(const struct cpumask *cpumask)
 static int multi_cpu_stop(void *data)
 {
 	struct multi_stop_data *msdata = data;
-	enum multi_stop_state curstate = MULTI_STOP_NONE;
+	enum multi_stop_state newstate, curstate = MULTI_STOP_NONE;
 	int cpu = smp_processor_id(), err = 0;
 	const struct cpumask *cpumask;
 	unsigned long flags;
@@ -210,8 +211,9 @@ static int multi_cpu_stop(void *data)
 	do {
 		/* Chill out and ensure we re-read multi_stop_state. */
 		stop_machine_yield(cpumask);
-		if (msdata->state != curstate) {
-			curstate = msdata->state;
+		newstate = READ_ONCE(msdata->state);
+		if (newstate != curstate) {
+			curstate = newstate;
 			switch (curstate) {
 			case MULTI_STOP_DISABLE_IRQ:
 				local_irq_disable();