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    Subject[PATCH 3.16 262/306] parisc: Fix race in pci-dma.c
    3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: John David Anglin <dave.anglin@bell.net>

    commit c0452fb9fb8f49c7d68ab9fa0ad092016be7b45f upstream.

    We are still troubled by occasional random segmentation faults and
    memory memory corruption on SMP machines. The causes quite a few
    package builds to fail on the Debian buildd machines for parisc. When
    gcc-6 failed to build three times in a row, I looked again at the TLB
    related code. I found a couple of issues. This is the first.

    In general, we need to ensure page table updates and corresponding TLB
    purges are atomic. The attached patch fixes an instance in pci-dma.c
    where the page table update was not guarded by the TLB lock.

    Tested on rp3440 and c8000. So far, no further random segmentation
    faults have been observed.

    Signed-off-by: John David Anglin <dave.anglin@bell.net>
    Signed-off-by: Helge Deller <deller@gmx.de>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    arch/parisc/kernel/pci-dma.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/parisc/kernel/pci-dma.c
    +++ b/arch/parisc/kernel/pci-dma.c
    @@ -95,8 +95,8 @@ static inline int map_pte_uncached(pte_t

    if (!pte_none(*pte))
    printk(KERN_ERR "map_pte_uncached: page already exists\n");
    - set_pte(pte, __mk_pte(*paddr_ptr, PAGE_KERNEL_UNC));
    purge_tlb_start(flags);
    + set_pte(pte, __mk_pte(*paddr_ptr, PAGE_KERNEL_UNC));
    pdtlb_kernel(orig_vaddr);
    purge_tlb_end(flags);
    vaddr += PAGE_SIZE;
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