linux-kernel - [PATCH] mm: Replace verify_mm_writelocked() by lockdep_assert_held

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Date:   Thu, 13 Dec 2018 14:38:05 -0500
From:   Waiman Long <longman@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH] 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 <longman@...hat.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