[GIT pull] core/urgent for 5.4-rc4

[Thomas Gleixner]

Linus,

please pull the latest core-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 
core-urgent-for-linus

up to:  b1fc58333575: stop_machine: Avoid potential race behaviour

A single fix, amending stop machine with WRITE/READ_ONCE() to address the
fallout of KCSAN.

Thanks,

        tglx

------------------>
Mark Rutland (1):
      stop_machine: Avoid potential race behaviour


 kernel/stop_machine.c | 10 ++++++----
 1 file 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 <t...@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();