[PATCH 01/21] workqueue: fix race condition in schedule_on_each_cpu()

Tejun Heo
2009-11-16T17:17:02Z

Commit 65a64464349883891e21e74af16c05d6e1eeb4e9 which allows
schedule_on_each_cpu() to be called from keventd added a race
condition. schedule_on_each_cpu() may race with cpu hotplug and end
up executing the function twice on a cpu.

Fix it by moving direct execution into the section protected with
get/put_online_cpus(). While at it, update code such that direct
execution is done after works have been scheduled for all other cpus
and drop unnecessary cpu != orig test from flush loop.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
---
kernel/workqueue.c | 28 +++++++++++++---------------
1 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1232814..67e526b 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -692,31 +692,29 @@ int schedule_on_each_cpu(work_func_t func)
if (!works)
return -ENOMEM;

+ get_online_cpus();
+
/*
- * when running in keventd don't schedule a work item on itself.
- * Can just call directly because the work queue is already bound.
- * This also is faster.
- * Make this a generic parameter for other workqueues?
+ * When running in keventd don't schedule a work item on
+ * itself. Can just call directly because the work queue is
+ * already bound. This also is faster.
*/
- if (current_is_keventd()) {
+ if (current_is_keventd())
orig = raw_smp_processor_id();
- INIT_WORK(per_cpu_ptr(works, orig), func);
- func(per_cpu_ptr(works, orig));
- }

- get_online_cpus();
for_each_online_cpu(cpu) {
struct work_struct *work = per_cpu_ptr(works, cpu);

- if (cpu == orig)
- continue;
INIT_WORK(work, func);
- schedule_work_on(cpu, work);
- }
- for_each_online_cpu(cpu) {
if (cpu != orig)
- flush_work(per_cpu_ptr(works, cpu));
+ schedule_work_on(cpu, work);
}
+ if (orig >= 0)
+ func(per_cpu_ptr(works, orig));
+
+ for_each_online_cpu(cpu)
+ flush_work(per_cpu_ptr(works, cpu));
+
put_online_cpus();
free_percpu(works);
return 0;
--
1.6.4.2