uprobes: __replace_page() should not use page_address_in_vma()
page_address_in_vma(old_page) in __replace_page() is ugly and wrong. The caller already knows the correct virtual address, this page was found by get_user_pages(vaddr). However, page_address_in_vma() can actually fail if page->mapping was cleared by __delete_from_page_cache() after get_user_pages() returns. But this means the race with page reclaim, write_opcode() should not fail, it should retry and read this page again. Probably the race with remove_mapping() is not possible due to page_freeze_refs() logic, but afaics at least shmem_writepage()->shmem_delete_from_page_cache() can clear ->mapping. We could change __replace_page() to return -EAGAIN in this case, but it would be better to simply use the caller's vaddr and rely on page_check_address(). Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Srikar Dronamraju <srikar.vnet.ibm.com> Cc: Anton Arapov <anton@redhat.com> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20120729182216.GA20311@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -127,22 +127,19 @@ static loff_t vma_address(struct vm_area_struct *vma, loff_t offset)
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* based on replace_page in mm/ksm.c
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*
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* @vma: vma that holds the pte pointing to page
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* @addr: address the old @page is mapped at
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* @page: the cowed page we are replacing by kpage
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* @kpage: the modified page we replace page by
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*
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* Returns 0 on success, -EFAULT on failure.
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*/
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static int __replace_page(struct vm_area_struct *vma, struct page *page, struct page *kpage)
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static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
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struct page *page, struct page *kpage)
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{
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struct mm_struct *mm = vma->vm_mm;
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unsigned long addr;
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spinlock_t *ptl;
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pte_t *ptep;
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addr = page_address_in_vma(page, vma);
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if (addr == -EFAULT)
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return -EFAULT;
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ptep = page_check_address(page, mm, addr, &ptl, 0);
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if (!ptep)
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return -EAGAIN;
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@ -243,7 +240,7 @@ retry:
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goto unlock_out;
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lock_page(new_page);
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ret = __replace_page(vma, old_page, new_page);
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ret = __replace_page(vma, vaddr, old_page, new_page);
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unlock_page(new_page);
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unlock_out:
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