lkml.org 
[lkml]   [2006]   [Mar]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Fix unlock_buffer() to work the same way as bit_unlock()
Chen, Kenneth W wrote:

>Nick Piggin wrote on Tuesday, March 28, 2006 12:11 AM
>
>>OK, that's fair enough and I guess you do need a barrier there.
>>However, should the mb__after barrier still remain? The comment
>>in wake_up_bit suggests yes, and there is similar code in
>>unlock_page.
>>
>
>Question on unlock_page:
>
>void fastcall unlock_page(struct page *page)
>{
> smp_mb__before_clear_bit();
> if (!TestClearPageLocked(page))
> BUG();
> smp_mb__after_clear_bit();
> wake_up_page(page, PG_locked);
>}
>
>Assuming test_and_clear_bit() on all arch does what the API is
>called for with full memory fence around the atomic op, why do
>you need smp_mb__before_clear_bit and smp_mb__after_clear_bit?
>Aren't they redundant?
>
>

Yep. I pointed this out earlier.

I'd say it may have initially just been a ClearPageLocked, and
was changed for debugging reasons.

We could instead change it to

BUG_ON(!PageLocked(page);
ClearPageLocked(page); /* this does clear_bit_for_unlock */
smp_mb__after_clear_bit_unlock();
wake_up_page

--

Send instant messages to your online friends http://au.messenger.yahoo.com

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-03-30 04:54    [W:0.692 / U:0.052 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site