From a3e8cc643d22d2c8ed36b9be7d9c9ca21efcf7f7 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Wed, 23 Feb 2011 21:39:49 -0800 Subject: [PATCH] mm: fix possible cause of a page_mapped BUG 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 Signed-off-by: Linus Torvalds --- mm/mremap.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/mm/mremap.c b/mm/mremap.c index 9925b6391b80..1de98d492ddc 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -94,9 +94,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, */ 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; } /* -- 2.34.1