On Fri, Jun 13, 2014 at 05:26:17PM +0100, Chris Wilson wrote:
> When using remap_pfn_range() from a fault handler, we are exposed to
> races between concurrent faults. Rather than hitting a BUG, report the
> error back to the caller, like vm_insert_pfn().
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> ---
> mm/memory.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 037b812a9531..6603a9e6a731 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2306,19 +2306,23 @@ static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
> {
> pte_t *pte;
> spinlock_t *ptl;
> + int ret = 0;
>
> pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
> if (!pte)
> return -ENOMEM;
> arch_enter_lazy_mmu_mode();
> do {
> - BUG_ON(!pte_none(*pte));
> + if (!pte_none(*pte)) {
> + ret = -EBUSY;
> + break;
> + }
> set_pte_at(mm, addr, pte, pte_mkspecial(pfn_pte(pfn, prot)));
> pfn++;
> } while (pte++, addr += PAGE_SIZE, addr != end);
> arch_leave_lazy_mmu_mode();
> pte_unmap_unlock(pte - 1, ptl);
Oh. That will want the EBUSY path to increment pte or we will try to
unmap the wrong page.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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