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Subject[PATCH 1/3] work_on_cpu: dont try to get_online_cpus() in work_on_cpu.
From: Rusty Russell <rusty@rustcorp.com.au>

Impact: remove potential circular lock dependency with cpu hotplug lock

This has caused more problems than it solved, with a pile of cpu
hotplug locking issues.

Followup patches will get_online_cpus() in callers that need it, but
if they don't do it they're no worse than before when they were using
set_cpus_allowed without locking.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Mike Travis <travis@sgi.com>
---
kernel/workqueue.c | 14 ++++----------
1 file changed, 4 insertions(+), 10 deletions(-)
--- linux-2.6-for-ingo.orig/kernel/workqueue.c
+++ linux-2.6-for-ingo/kernel/workqueue.c
@@ -991,8 +991,8 @@ static void do_work_for_cpu(struct work_
* @fn: the function to run
* @arg: the function arg
*
- * This will return -EINVAL in the cpu is not online, or the return value
- * of @fn otherwise.
+ * This will return the value @fn returns.
+ * It is up to the caller to ensure that the cpu doesn't go offline.
*/
long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
{
@@ -1001,14 +1001,8 @@ long work_on_cpu(unsigned int cpu, long
INIT_WORK(&wfc.work, do_work_for_cpu);
wfc.fn = fn;
wfc.arg = arg;
- get_online_cpus();
- if (unlikely(!cpu_online(cpu)))
- wfc.ret = -EINVAL;
- else {
- schedule_work_on(cpu, &wfc.work);
- flush_work(&wfc.work);
- }
- put_online_cpus();
+ schedule_work_on(cpu, &wfc.work);
+ flush_work(&wfc.work);

return wfc.ret;
}
--


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