Re: [resend] powerpc/64s: fix page table fragment refcount race vs speculative references

On Fri, 2018-07-27 at 11:48:17 UTC, Nicholas Piggin wrote:

The page table fragment allocator uses the main page refcount racily
with respect to speculative references. A customer observed a BUG due
to page table page refcount underflow in the fragment allocator. This
can be caused by the fragment allocator set_page_count stomping on a
speculative reference, and then the speculative failure handler
decrements the new reference, and the underflow eventually pops when
the page tables are freed.

Fix this by using a dedicated field in the struct page for the page
table fragment allocator.

Fixes: 5c1f6ee9a31c ("powerpc: Reduce PTE table memory wastage")
Reviewed-by: Aneesh Kumar K.V <redacted>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/4231aba000f5a4583dd9f67057aadb

cheers