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.
Andrea
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This archive was generated by hypermail 2b29 : Mon Jul 15 2002 - 22:00:21 EST