Since we limit vm_refcnt at VMA_REF_LIMIT and it's smaller than
VMA_LOCK_OFFSET, there is no need to check again if VMA_LOCK_OFFSET bit
is set. Remove the extra check and add a clarifying comment.
Fixes: e8f32ff00a66 ("mm: replace vm_lock and detached flag with a reference count")
Suggested-by: Wei Yang <richard.weiyang@xxxxxxxxx>
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
Applies over mm-unstable
include/linux/mm.h | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 486638d22fc6..b5f262fc7dc5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -747,7 +747,11 @@ static inline bool vma_start_read(struct mm_struct *mm, struct vm_area_struct *v
rwsem_acquire_read(&vma->vmlock_dep_map, 0, 0, _RET_IP_);
- /* Limit at VMA_REF_LIMIT to leave one count for a writer */
+ /*
+ * Limit at VMA_REF_LIMIT to leave one count for a writer.
+ * If VMA_LOCK_OFFSET is set, __refcount_inc_not_zero_limited() will fail
+ * because VMA_REF_LIMIT is less than VMA_LOCK_OFFSET.
+ */
if (unlikely(!__refcount_inc_not_zero_limited(&vma->vm_refcnt, &oldcnt,
VMA_REF_LIMIT))) {
rwsem_release(&vma->vmlock_dep_map, _RET_IP_);
@@ -766,8 +770,7 @@ static inline bool vma_start_read(struct mm_struct *mm, struct vm_area_struct *v
* after it has been unlocked.
* This pairs with RELEASE semantics in vma_end_write_all().
*/
- if (unlikely(oldcnt & VMA_LOCK_OFFSET ||
- vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) {
+ if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) {
vma_refcount_put(vma);
return false;
}
base-commit: f349e79bfbf3abfade8011797ff6d0d47b67dab7
--
2.47.1.613.gc27f4b7a9f-goog
