On 01/04, Srivatsa Vaddagiri wrote:
>
> On Mon, Dec 18, 2006 at 01:34:16AM +0300, Oleg Nesterov wrote:
> > void fastcall flush_workqueue(struct workqueue_struct *wq)
> > {
> > - might_sleep();
> > -
> > + mutex_lock(&workqueue_mutex);
> > if (is_single_threaded(wq)) {
> > /* Always use first cpu's area. */
> > - flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu),
> > - -1);
> > + flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu));
> > } else {
> > int cpu;
> >
> > - mutex_lock(&workqueue_mutex);
> > for_each_online_cpu(cpu)
>
>
> Can compiler optimizations lead to cpu_online_map being cached in a register
> while running this loop? AFAICS cpu_online_map is not declared to be
> volatile.
But it is not const either,
> If it can be cached,
I believe this would be a compiler's bug. Let's take a more simple example,
while (!condition)
schedule();
What if compiler will cache the value of global 'condition' ?
then we have the danger of invoking
> flush_cpu_workqueue() on a dead cpu (because flush_cpu_workqueue drops
> workqueue_mutex, cpu hp events can change cpu_online_map while we are in
> flush_cpu_workqueue).
Oleg.
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