[PATCH] mm: Replace verify_mm_writelocked() by lockdep_assert_held_exclusive()

Waiman Long
2018-12-13T19:38:30Z

Using down_read_trylock() to check if a task holds a write lock on
a rwsem is not reliable. A task can hold a read lock on a rwsem and
down_read_trylock() can fail if a writer is waiting in the wait queue.
So use lockdep_assert_held_exclusive() instead which can do the right
check when CONFIG_LOCKDEP is on.

Signed-off-by: Waiman Long <longman@redhat.com>
---
mm/mmap.c | 12 +-----------
1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 6c04292..62a5593 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2962,16 +2962,6 @@ int vm_munmap(unsigned long start, size_t len)
return ret;
}

-static inline void verify_mm_writelocked(struct mm_struct *mm)
-{
-#ifdef CONFIG_DEBUG_VM
- if (unlikely(down_read_trylock(&mm->mmap_sem))) {
- WARN_ON(1);
- up_read(&mm->mmap_sem);
- }
-#endif
-}
-
/*
* this is really a simplified "do_mmap". it only handles
* anonymous maps. eventually we may be able to do some
@@ -3002,7 +2992,7 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
* mm->mmap_sem is required to protect against another thread
* changing the mappings in case we sleep.
*/
- verify_mm_writelocked(mm);
+ lockdep_assert_held_exclusive(&mm->mmap_sem);

/*
* Clear old maps. this also does some error checking for us
--
1.8.3.1