Messages in this thread Patch in this message | | | Date | Wed, 23 Feb 2011 21:39:49 -0800 (PST) | From | Hugh Dickins <> | Subject | [PATCH] mm: fix possible cause of a page_mapped BUG |
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Robert Swiecki reported a BUG_ON(page_mapped) from a fuzzer, punching a hole with madvise(,, MADV_REMOVE). That path is under mutex, and cannot be explained by lack of serialization in unmap_mapping_range().
Reviewing the code, I found one place where vm_truncate_count handling should have been updated, when I switched at the last minute from one way of managing the restart_addr to another: mremap move changes the virtual addresses, so it ought to adjust the restart_addr.
But rather than exporting the notion of restart_addr from memory.c, or converting to restart_pgoff throughout, simply reset vm_truncate_count to 0 to force a rescan if mremap move races with preempted truncation.
We have no confirmation that this fixes Robert's BUG, but it is a fix that's worth making anyway.
Signed-off-by: Hugh Dickins <hughd@google.com> ---
mm/mremap.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
--- 2.6.38-rc6/mm/mremap.c 2011-01-18 22:04:56.000000000 -0800 +++ linux/mm/mremap.c 2011-02-23 15:29:52.000000000 -0800 @@ -94,9 +94,7 @@ static void move_ptes(struct vm_area_str */ mapping = vma->vm_file->f_mapping; spin_lock(&mapping->i_mmap_lock); - if (new_vma->vm_truncate_count && - new_vma->vm_truncate_count != vma->vm_truncate_count) - new_vma->vm_truncate_count = 0; + new_vma->vm_truncate_count = 0; } /*
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