linux-kernel - [PATCH RESEND v3 08/10] mm/vma: improve and document __is_vma_write

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Message-ID: <70dcf80f79ecd00a750ea17101061b0949119429.1769086312.git.lorenzo.stoakes@oracle.com>
Date: Thu, 22 Jan 2026 13:02:00 +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: [PATCH RESEND v3 08/10] mm/vma: improve and document __is_vma_write_locked()

The function is a little confusing, clean it up a little then add a
descriptive comment.

No functional change intended.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 include/linux/mmap_lock.h | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 873bc5f3c97c..b00d34b5ad10 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -252,17 +252,30 @@ static inline void vma_end_read(struct vm_area_struct *vma)
 	vma_refcount_put(vma);
 }

-/* WARNING! Can only be used if mmap_lock is expected to be write-locked */
-static inline bool __is_vma_write_locked(struct vm_area_struct *vma, unsigned int *mm_lock_seq)
+/*
+ * Determine whether a VMA is write-locked. Must be invoked ONLY if the mmap
+ * write lock is held.
+ *
+ * Returns true if write-locked, otherwise false.
+ *
+ * Note that mm_lock_seq is updated only if the VMA is NOT write-locked.
+ */
+static inline bool __is_vma_write_locked(struct vm_area_struct *vma,
+					 unsigned int *mm_lock_seq)
 {
-	mmap_assert_write_locked(vma->vm_mm);
+	struct mm_struct *mm = vma->vm_mm;
+	const unsigned int seq = mm->mm_lock_seq.sequence;
+
+	mmap_assert_write_locked(mm);

 	/*
 	 * current task is holding mmap_write_lock, both vma->vm_lock_seq and
 	 * mm->mm_lock_seq can't be concurrently modified.
 	 */
-	*mm_lock_seq = vma->vm_mm->mm_lock_seq.sequence;
-	return (vma->vm_lock_seq == *mm_lock_seq);
+	if (vma->vm_lock_seq == seq)
+		return true;
+	*mm_lock_seq = seq;
+	return false;
 }

 int __vma_start_write(struct vm_area_struct *vma, unsigned int mm_lock_seq,
--
2.52.0