On Wed, May 14, 2014 at 06:11:52PM +0200, Oleg Nesterov wrote:
> The subsequent discussion was "off-topic", and it seems that the patch
> itself needs a bit more discussion,
>
> On 05/13, Peter Zijlstra wrote:
> >
> > On Tue, May 13, 2014 at 01:53:13PM +0100, Mel Gorman wrote:
> > > On Tue, May 13, 2014 at 10:45:50AM +0100, Mel Gorman wrote:
> > > > void unlock_page(struct page *page)
> > > > {
> > > > + wait_queue_head_t *wqh = clear_page_waiters(page);
> > > > +
> > > > VM_BUG_ON_PAGE(!PageLocked(page), page);
> > > > +
> > > > + /*
> > > > + * No additional barrier needed due to clear_bit_unlock
> > > > barriering all updates
> > > > + * before waking waiters
> > > > + */
> > > > clear_bit_unlock(PG_locked, &page->flags);
> > > > - smp_mb__after_clear_bit();
> > > > - wake_up_page(page, PG_locked);
> > >
> > > This is wrong.
>
> Yes,
>
> > > The smp_mb__after_clear_bit() is still required to ensure
> > > that the cleared bit is visible before the wakeup on all architectures.
>
> But note that "the cleared bit is visible before the wakeup" is confusing.
> I mean, we do not need mb() before __wake_up(). We need it only because
> __wake_up_bit() checks waitqueue_active().
>
>
> And at least
>
> fs/cachefiles/namei.c:cachefiles_delete_object()
> fs/block_dev.c:blkdev_get()
> kernel/signal.c:task_clear_jobctl_trapping()
> security/keys/gc.c:key_garbage_collector()
>
> look obviously wrong.
>
> I would be happy to send the fix, but do I need to split it per-file?
> Given that it is trivial, perhaps I can send a single patch?Since its all the same issue a single patch would be fine I think.
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