[PATCH 2/5] HWPOISON: fix tasklist_lock/anon_vma locking order

From: Wu Fengguang
Date: Thu Jun 11 2009 - 10:54:13 EST

To avoid possible deadlock. Proposed by Nick Piggin:

You have tasklist_lock(R) nesting outside i_mmap_lock, and inside anon_vma
lock. And anon_vma lock nests inside i_mmap_lock.

This seems fragile. If rwlocks ever become FIFO or tasklist_lock changes
type (maybe -rt kernels do it), then you could have a task holding
anon_vma lock and waiting for tasklist_lock, and another holding tasklist
lock and waiting for i_mmap_lock, and another holding i_mmap_lock and
waiting for anon_vma lock.

CC: Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
mm/memory-failure.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

--- sound-2.6.orig/mm/memory-failure.c
+++ sound-2.6/mm/memory-failure.c
@@ -215,12 +215,14 @@ static void collect_procs_anon(struct pa
struct vm_area_struct *vma;
struct task_struct *tsk;
- struct anon_vma *av = page_lock_anon_vma(page);
+ struct anon_vma *av;

+ read_lock(&tasklist_lock);
+ av = page_lock_anon_vma(page);
if (av == NULL) /* Not actually mapped anymore */
- return;
+ goto out;

- read_lock(&tasklist_lock);
for_each_process (tsk) {
if (!tsk->mm)
@@ -230,6 +232,7 @@ static void collect_procs_anon(struct pa


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