Messages in this thread |  | | | Date | Thu, 11 Jul 2002 21:51:29 -0300 (BRT) | | From | Marcelo Tosatti <> | | Subject | Re: fsync fixes for 2.4 |
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On Fri, 12 Jul 2002, Andrea Arcangeli wrote:
> On Thu, Jul 11, 2002 at 05:21:24PM -0300, Marcelo Tosatti wrote: > > > > > > 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? > > yes, that's it.
So I'm just going to add wait_on_page() on fsync_buffers_list() before the ll_rw_block().
Nothing else, since all of the other stuff on your patch seems to be improvements rather than bug fixes. ACK?
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