On 03/25/2015 06:38 AM, Boaz Harrosh wrote:
> /*
> * This routine handles present pages, when users try to write
> * to a shared page. It is done by copying the page to a new address
> @@ -2025,8 +2042,17 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
> * accounting on raw pfn maps.
> */
> if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
> - (VM_WRITE|VM_SHARED))
> + (VM_WRITE|VM_SHARED)) {
> + pte_unmap_unlock(page_table, ptl);
> + ret = do_pfn_mkwrite(vma, address);
> + if (ret & VM_FAULT_ERROR)
> + return ret;
> + page_table = pte_offset_map_lock(mm, pmd, address,
> + &ptl);
> + if (!pte_same(*page_table, orig_pte))
> + goto unlock;
> goto reuse;
> + }
> goto gotten;
> }
This adds a lock release/reacquire in a place where the lock was
previously just held. Could you explain a bit why this is safe?
Also, that pte_same() check looks a bit fragile. It seems like it would
fail if the hardware, for instance, set the accessed bit in here
somewhere. Is that what we want?
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