On Thu, 3 May 2007, Nick Piggin wrote: > >>@@ -568,6 +570,11 @@ __lock_page (diff -p would tell us!) > > > { > > > DEFINE_WAIT_BIT(wait, &page->flags, PG_locked); > > > > > >+ set_bit(PG_waiters, &page->flags); > > >+ if (unlikely(!TestSetPageLocked(page))) { > > > > What happens if another cpu is coming through __lock_page at the > > same time, did its set_bit, now finds PageLocked, and so proceeds > > to the __wait_on_bit_lock? But this cpu now clears PG_waiters, > > so this task's unlock_page won't wake the other? > > You're right, we can't clear the bit here. Doubt it mattered much anyway?
Ah yes, that's a good easy answer. In fact, just remove this whole test and block (we already tried TestSetPageLocked outside just a short while ago, so this repeat won't often save anything). > > BTW. I also forgot an smp_mb__after_clear_bit() before the wake_up_page > above... that barrier is in the slow path as well though, so it shouldn't > matter either. I vaguely wondered how such barriers had managed to dissolve away, but cranking my brain up to think about barriers takes far too long. > > >+ clear_bit(PG_waiters, &page->flags); > > >+ return; > > >+ } > > > __wait_on_bit_lock(page_waitqueue(page), &wait, sync_page, > > > TASK_UNINTERRUPTIBLE); > >> } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/