Messages in this thread Patch in this message | | | Date | Fri, 11 Mar 2011 12:40:06 -0800 | From | Greg KH <> | Subject | [05/17] mm: fix possible cause of a page_mapped BUG |
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2.6.32-longterm review patch. If anyone has any objections, please let us know.
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From: Hugh Dickins <hughd@google.com>
commit a3e8cc643d22d2c8ed36b9be7d9c9ca21efcf7f7 upstream.
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> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Kerin Millar <kerframil@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- mm/mremap.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
--- a/mm/mremap.c +++ b/mm/mremap.c @@ -92,9 +92,7 @@ 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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