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mm: Replace verify_mm_writelocked() by lockdep_assert_held_exclusive()

PATCH In review Waiman Long 2 participants 2 messages Dec 13, 2018

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Waiman Long

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#0 lore raw

PATCH 1/1 mm: Replace verify_mm_writelocked() by lockdep_assert_held_exclusive()

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 <[email protected]>
---
 mm/mmap.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)
mm/mmap.c +1 -11
index 6c04292..62a5593 100644
@@ -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
Signature · 1 line
1.8.3.1
#1 lore raw
Quoted 8 lines · Waiman Long

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 <[email protected]>

There's already a patch in mmotm removing this completely:
https://www.ozlabs.org/~akpm/mmots/broken-out/mm-mmap-remove-verify_mm_writelocked.patch

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