| From 682a3c5552e11a3ffd20e15021469b212b6e5d91 Mon Sep 17 00:00:00 2001 |
| From: Hugh Dickins <hughd@google.com> |
| Date: Wed, 23 Feb 2011 21:39:49 -0800 |
| Subject: [PATCH] mm: fix possible cause of a page_mapped BUG |
| |
| 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> |
| Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/mm/mremap.c b/mm/mremap.c |
| index cde56ee..10d5f62 100644 |
| --- a/mm/mremap.c |
| +++ b/mm/mremap.c |
| @@ -91,9 +91,7 @@ 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; |
| } |
| |
| /* |
| -- |
| 1.7.4.4 |
| |
