Commit f756d5e2 authored by Nathan Lynch's avatar Nathan Lynch Committed by Linus Torvalds
Browse files

[PATCH] fix workqueue oops during cpu offline

Use first_cpu(cpu_possible_map) for the single-thread workqueue case.  We
used to hardcode 0, but that broke on systems where !cpu_possible(0) when
workqueue_struct->cpu_workqueue_struct was changed from a static array to

Commit id bce61dd4

 ("Fix hardcoded cpu=0 in
workqueue for per_cpu_ptr() calls") fixed that for Ben's funky sparc64
system, but it regressed my Power5.  Offlining cpu 0 oopses upon the next
call to queue_work for a single-thread workqueue, because now we try to
manipulate per_cpu_ptr(wq->cpu_wq, 1), which is uninitialized.

So we need to establish an unchanging "slot" for single-thread workqueues
which will have a valid percpu allocation.  Since alloc_percpu keys off of
cpu_possible_map, which must not change after initialization, make this
slot == first_cpu(cpu_possible_map).

Signed-off-by: default avatarNathan Lynch <>
Cc: <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 945f390f
......@@ -29,7 +29,8 @@
#include <linux/kthread.h>
* The per-CPU workqueue (if single thread, we always use cpu 0's).
* The per-CPU workqueue (if single thread, we always use the first
* possible cpu).
* The sequence counters are for flush_scheduled_work(). It wants to wait
* until until all currently-scheduled works are completed, but it doesn't
......@@ -69,6 +70,8 @@ struct workqueue_struct {
static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
static int singlethread_cpu;
/* If it's single threaded, it isn't in the list of workqueues. */
static inline int is_single_threaded(struct workqueue_struct *wq)
......@@ -102,7 +105,7 @@ int fastcall queue_work(struct workqueue_struct *wq, struct work_struct *work)
if (!test_and_set_bit(0, &work->pending)) {
if (unlikely(is_single_threaded(wq)))
cpu = any_online_cpu(cpu_online_map);
cpu = singlethread_cpu;
__queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
ret = 1;
......@@ -118,7 +121,7 @@ static void delayed_work_timer_fn(unsigned long __data)
int cpu = smp_processor_id();
if (unlikely(is_single_threaded(wq)))
cpu = any_online_cpu(cpu_online_map);
cpu = singlethread_cpu;
__queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
......@@ -267,7 +270,7 @@ void fastcall flush_workqueue(struct workqueue_struct *wq)
if (is_single_threaded(wq)) {
/* Always use first cpu's area. */
flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, any_online_cpu(cpu_online_map)));
flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu));
} else {
int cpu;
......@@ -325,7 +328,7 @@ struct workqueue_struct *__create_workqueue(const char *name,
if (singlethread) {
p = create_workqueue_thread(wq, any_online_cpu(cpu_online_map));
p = create_workqueue_thread(wq, singlethread_cpu);
if (!p)
destroy = 1;
......@@ -379,7 +382,7 @@ void destroy_workqueue(struct workqueue_struct *wq)
/* We don't need the distraction of CPUs appearing and vanishing. */
if (is_single_threaded(wq))
cleanup_workqueue_thread(wq, any_online_cpu(cpu_online_map));
cleanup_workqueue_thread(wq, singlethread_cpu);
else {
cleanup_workqueue_thread(wq, cpu);
......@@ -567,6 +570,7 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
void init_workqueues(void)
singlethread_cpu = first_cpu(cpu_possible_map);
hotcpu_notifier(workqueue_cpu_callback, 0);
keventd_wq = create_workqueue("events");
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