[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
alloc_percpu.
Commit id bce61dd49d6ba7799be2de17c772e4c701558f14 ("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: Nathan Lynch <ntl@pobox.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e72fb64..82c4fa7 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -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 @@
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 @@
if (!test_and_set_bit(0, &work->pending)) {
if (unlikely(is_single_threaded(wq)))
- cpu = any_online_cpu(cpu_online_map);
+ cpu = singlethread_cpu;
BUG_ON(!list_empty(&work->entry));
__queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
ret = 1;
@@ -118,7 +121,7 @@
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 @@
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 @@
lock_cpu_hotplug();
if (singlethread) {
INIT_LIST_HEAD(&wq->list);
- p = create_workqueue_thread(wq, any_online_cpu(cpu_online_map));
+ p = create_workqueue_thread(wq, singlethread_cpu);
if (!p)
destroy = 1;
else
@@ -379,7 +382,7 @@
/* We don't need the distraction of CPUs appearing and vanishing. */
lock_cpu_hotplug();
if (is_single_threaded(wq))
- cleanup_workqueue_thread(wq, any_online_cpu(cpu_online_map));
+ cleanup_workqueue_thread(wq, singlethread_cpu);
else {
for_each_online_cpu(cpu)
cleanup_workqueue_thread(wq, cpu);
@@ -567,6 +570,7 @@
void init_workqueues(void)
{
+ singlethread_cpu = first_cpu(cpu_possible_map);
hotcpu_notifier(workqueue_cpu_callback, 0);
keventd_wq = create_workqueue("events");
BUG_ON(!keventd_wq);