lkml.org 
[lkml]   [2002]   [Jul]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: fsync fixes for 2.4


On Wed, 10 Jul 2002, Andrea Arcangeli wrote:

> At polyserve they found a severe problem with fsync in 2.4.
>
> In short the write_buffer (ll_rw_block of mainline) is a noop if old I/O
> is in flight. You know the buffer can be made dirty while I/O is in
> flight, and in such case fsync would return without flushing the dirty
> buffers at all. Their proposed fix is strightforward, just a
> wait_on_buffer before the ll_rw_block will guarantee somebody marked the
> bh locked _after_ we wrote to it.

From what I can see the problem goes like:


thread1 thread2
writepage(page) (marks the buffers clean, page is
locked for IO)

mark_buffer_dirty()

fsync()

fsync_buffers_list() finds
the dirtied buffer, but since
its locked ll_rw_block() returns
without queueing the data.

fsync_buffers_list() waits on the writepage()'s
write to return but not on latest data write.


Is that what you mean or I'm misunderstanding something?

-
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: 2005-03-22 13:27    [from the cache]
©2003-2011 Jasper Spaans. Advertise on this site