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

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

1 files changed, 6 insertions, 4 deletions

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index c7031a22aa7b..998d50ee2d9b 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 <tj@kernel.org>
  */
+#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();