On Tue, Oct 16, 2012 at 9:49 PM, David Rientjes [off-list ref] wrote:

On Tue, 16 Oct 2012, KOSAKI Motohiro wrote:

quoted

quoted

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 0b78fb9..d04a8a5 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c

@@ -1536,9 +1536,8 @@ asmlinkage long compat_sys_mbind(compat_ulong_t start, compat_ulong_t len,
  *
  * Returns effective policy for a VMA at specified address.
  * Falls back to @task or system default policy, as necessary.
- * Current or other task's task mempolicy and non-shared vma policies
- * are protected by the task's mmap_sem, which must be held for read by
- * the caller.
+ * Current or other task's task mempolicy and non-shared vma policies must be
+ * protected by task_lock(task) by the caller.

This is not correct. mmap_sem is needed for protecting vma. task_lock()
is needed to close vs exit race only when task != current. In other word,
caller must held both mmap_sem and task_lock if task != current.

The comment is specifically addressing non-shared vma policies, you do not
need to hold mmap_sem to access another thread's mempolicy.

I didn't say old comment is true. I just only your new comment also false.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>