On Tue, 27 Apr 2010 09:59:51 +0100 Mel Gorman <mel@xxxxxxxxx> wrote: > On Tue, Apr 27, 2010 at 12:50:40PM +0900, KAMEZAWA Hiroyuki wrote: > > On Tue, 27 Apr 2010 09:07:06 +0900 > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > > > > On Mon, 26 Apr 2010 23:37:58 +0100 > > > Mel Gorman <mel@xxxxxxxxx> wrote: > > > > > > > vma_adjust() is updating anon VMA information without any locks taken. > > > > In contrast, file-backed mappings use the i_mmap_lock and this lack of > > > > locking can result in races with page migration. During rmap_walk(), > > > > vma_address() can return -EFAULT for an address that will soon be valid. > > > > This leaves a dangling migration PTE behind which can later cause a BUG_ON > > > > to trigger when the page is faulted in. > > > > > > > > With the recent anon_vma changes, there can be more than one anon_vma->lock > > > > that can be taken in a anon_vma_chain but a second lock cannot be spinned > > > > upon in case of deadlock. Instead, the rmap walker tries to take locks of > > > > different anon_vma's. If the attempt fails, the operation is restarted. > > > > > > > > Signed-off-by: Mel Gorman <mel@xxxxxxxxx> > > > > > > Ok, acquiring vma->anon_vma->spin_lock always sounds very safe. > > > (but slow.) > > > > > > I'll test this, too. > > > > > > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > > > > > > > Sorry. reproduced. It seems the same bug before patch. > > mapcount 1 -> unmap -> remap -> mapcount 0. And it was SwapCache. > > > > Same here, reproduced after 18 hours. > Hmm. It seems rmap_one() is called and the race is not in vma_address() but in remap_migration_pte(). So, I added more hooks for debug..but not reproduced yet. (But I doubt my debug code, too ;) But it seems strange to have a race in remap_migration_pte(), so, I doubt my debug code, too. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>