Messages in this thread | | | Date | Fri, 6 Mar 2009 22:55:25 +0000 | From | Russell King - ARM Linux <> | Subject | Re: cache aliasing in dup_mmap |
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On Fri, Mar 06, 2009 at 05:26:24PM -0500, Steven Walter wrote: > I've been tracking down an instance of userspace data corruption, and I > believe I have found a window during fork where data can be lost. The > corruption is occurring on an ARMv5 system with VIVT caches. Here's the > scenario in question. Thread A is forking, Thread B is running in > userspace:
With VIVT caches, you're missing a few things here:
> Thread A: flush_cache_mm (dup_mmap)
-- cache written back and invalidated
> Thread B: writes to a page in the above mm
-- cache written back and invalidated
> Thread A: pte_wrprotect the above page (copy_one_pte)
-- cache written back and invalidated
> Thread B: writes to the same page again > > During thread B's second write, he'll take a fault and enter the do_wp_page > case. We'll end up calling copy_page, which notably uses the kernel virtual > addresses for the old and new pages. This means that the new page does not > necessarily have the data from the first write.
Given the additional flushing I've mentioned above, where could the problem be?
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