Messages in this thread | | | Date | Sun, 22 Jun 2003 23:32:35 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] Fix vmtruncate race and distributed filesystem race |
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"Paul E. McKenney" <paulmck@us.ibm.com> wrote: > > > but you can't trap this with a single counter increment in do_truncate: > > > > CPU 0 CPU 1 > > ---------- ----------- > > do_no_page > > truncate
i_size = new_i_size;
> > increment counter > > read counter > > ->nopage
check i_size
> > vmtruncate > > read counter again -> different so retry > > > > thanks to the second counter increment after vmtruncate in my fix, the > > above race couldn't happen. > > The trick is that CPU 0 is expected to have updated the filesystem's > idea of what pages are available before calling vmtruncate, > invalidate_mmap_range() or whichever.
i_size has been updated, and filemap_nopage() will return NULL.
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