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

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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
This commit is contained in:
Linus Torvalds 2019-10-20 06:22:25 -04:00
commit 589f1222e0
1 changed files with 6 additions and 4 deletions
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10
kernel/stop_machine.c
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@ -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();