linux-kernel - Re: [PATCH v4 09/10] mm/vma: update vma_assert

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Message-ID: <7c4b722e-604b-4b20-8e33-03d2f8d55407@lucifer.local>
Date: Mon, 26 Jan 2026 17:37:08 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Shakeel Butt <shakeel.butt@...ux.dev>, Jann Horn <jannh@...gle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-rt-devel@...ts.linux.dev, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>, Waiman Long <longman@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Clark Williams <clrkwllms@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v4 09/10] mm/vma: update vma_assert_locked() to use
 lockdep

Hi Andrew,

Could you apply the attached fix-patch to apply Vlasta's suggestion, and to
avoid unnecessary ifdeffery.

Could you also adjust the original commit message to append the below?
Thanks!

-->
Additionally, abstract references to vma->vmlock_dep_map by introducing a
macro helper __vma_lockdep_map() which accesses this field if lockdep is
enabled.

Since lock_is_held() is specified as an extern function if lockdep is
disabled, we can simply have __vma_lockdep_map() defined as NULL in this
case, and then use IS_ENABLED(CONFIG_LOCKDEP) to avoid ugly ifdeffery.
<--

Cheers, Lorenzo


----8<----
>From 9fb6dbe821c87759b269ddc926343d1f9c26db2a Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Date: Mon, 26 Jan 2026 16:40:34 +0000
Subject: [PATCH] fix

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 include/linux/mmap_lock.h | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 4a0aafc66c5d..160c572c1798 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -78,6 +78,12 @@ static inline void mmap_assert_write_locked(const struct mm_struct *mm)

 #ifdef CONFIG_PER_VMA_LOCK

+#ifdef CONFIG_LOCKDEP
+#define __vma_lockdep_map(vma) (&vma->vmlock_dep_map)
+#else
+#define __vma_lockdep_map(vma) NULL
+#endif
+
 /*
  * VMA locks do not behave like most ordinary locks found in the kernel, so we
  * cannot quite have full lockdep tracking in the way we would ideally prefer.
@@ -98,16 +104,16 @@ static inline void mmap_assert_write_locked(const struct mm_struct *mm)
  * so we utilise lockdep to do so.
  */
 #define __vma_lockdep_acquire_read(vma) \
-	lock_acquire_shared(&vma->vmlock_dep_map, 0, 1, NULL, _RET_IP_)
+	lock_acquire_shared(__vma_lockdep_map(vma), 0, 1, NULL, _RET_IP_)
 #define __vma_lockdep_release_read(vma) \
-	lock_release(&vma->vmlock_dep_map, _RET_IP_)
+	lock_release(__vma_lockdep_map(vma), _RET_IP_)
 #define __vma_lockdep_acquire_exclusive(vma) \
-	lock_acquire_exclusive(&vma->vmlock_dep_map, 0, 0, NULL, _RET_IP_)
+	lock_acquire_exclusive(__vma_lockdep_map(vma), 0, 0, NULL, _RET_IP_)
 #define __vma_lockdep_release_exclusive(vma) \
-	lock_release(&vma->vmlock_dep_map, _RET_IP_)
+	lock_release(__vma_lockdep_map(vma), _RET_IP_)
 /* Only meaningful if CONFIG_LOCK_STAT is defined. */
 #define __vma_lockdep_stat_mark_acquired(vma) \
-	lock_acquired(&vma->vmlock_dep_map, _RET_IP_)
+	lock_acquired(__vma_lockdep_map(vma), _RET_IP_)

 static inline void mm_lock_seqcount_init(struct mm_struct *mm)
 {
@@ -146,7 +152,7 @@ static inline void vma_lock_init(struct vm_area_struct *vma, bool reset_refcnt)
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	static struct lock_class_key lockdep_key;

-	lockdep_init_map(&vma->vmlock_dep_map, "vm_lock", &lockdep_key, 0);
+	lockdep_init_map(__vma_lockdep_map(vma), "vm_lock", &lockdep_key, 0);
 #endif
 	if (reset_refcnt)
 		refcount_set(&vma->vm_refcnt, 0);
@@ -340,14 +346,11 @@ static inline void vma_assert_locked(struct vm_area_struct *vma)
 {
 	unsigned int refcnt;

-	/*
-	* If read-locked or currently excluding readers, then the VMA is
-	* locked.
-	*/
-#ifdef CONFIG_LOCKDEP
-	if (lock_is_held(&vma->vmlock_dep_map))
+	if (IS_ENABLED(CONFIG_LOCKDEP)) {
+		if (!lock_is_held(__vma_lockdep_map(vma)))
+			vma_assert_write_locked(vma);
 		return;
-#endif
+	}

 	/*
 	* See the comment describing the vm_area_struct->vm_refcnt field for
--
2.52.0