race between kmap shootdown and cache maintenance

[Gary King]

I have seen some instability with highmem enabled on Tegra 2 systems (Cortex A9 SMP), where ocassionally the kernel will panic with unservicable page faults from flush_dcache_page, at an address half-way through a kmapped page.

I think this patch addresses the root cause: the cache maintenance code doesn't increase the reference count of the kmap, so another thread may kunmap the last reference and zap the corresponding PTE.

- Gary

Gary King
gking at nvidia.com




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