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>

1 files changed, 4 insertions, 7 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index a2b32a51d0a2..6fda7996892b 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -127,22 +127,19 @@ static loff_t vma_address(struct vm_area_struct *vma, loff_t offset)
  * based on replace_page in mm/ksm.c
  *
  * @vma:      vma that holds the pte pointing to page
+ * @addr:     address the old @page is mapped at
  * @page:     the cowed page we are replacing by kpage
  * @kpage:    the modified page we replace page by
  *
  * Returns 0 on success, -EFAULT on failure.
  */
-static int __replace_page(struct vm_area_struct *vma, struct page *page, struct page *kpage)
+static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
+                                struct page *page, struct page *kpage)
 {
         struct mm_struct *mm = vma->vm_mm;
-        unsigned long addr;
         spinlock_t *ptl;
         pte_t *ptep;
 
-        addr = page_address_in_vma(page, vma);
-        if (addr == -EFAULT)
-                return -EFAULT;
-
         ptep = page_check_address(page, mm, addr, &ptl, 0);
         if (!ptep)
                 return -EAGAIN;
@@ -243,7 +240,7 @@ retry:
                 goto unlock_out;
 
         lock_page(new_page);
-        ret = __replace_page(vma, old_page, new_page);
+        ret = __replace_page(vma, vaddr, old_page, new_page);
         unlock_page(new_page);
 
 unlock_out: