[PATCH v3 tip/perf/core 2/4] mm: switch to 64-bit mm_lock_seq/vm_lock_seq on 64-bit architectures

[Andrii Nakryiko]

To increase mm->mm_lock_seq robustness, switch it from int to long, so
that it's a 64-bit counter on 64-bit systems and we can stop worrying
about it wrapping around in just ~4 billion iterations. Same goes for
VMA's matching vm_lock_seq, which is derived from mm_lock_seq.

I didn't use __u64 outright to keep 32-bit architectures unaffected, but
if it seems important enough, I have nothing against using __u64.

Suggested-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
 include/linux/mm.h        | 6 +++---
 include/linux/mm_types.h  | 4 ++--
 include/linux/mmap_lock.h | 8 ++++----
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ecf63d2b0582..97819437832e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -730,7 +730,7 @@ static inline void vma_end_read(struct vm_area_struct *vma)
 }
 
 /* WARNING! Can only be used if mmap_lock is expected to be write-locked */
-static bool __is_vma_write_locked(struct vm_area_struct *vma, int *mm_lock_seq)
+static bool __is_vma_write_locked(struct vm_area_struct *vma, long *mm_lock_seq)
 {
 	mmap_assert_write_locked(vma->vm_mm);
 
@@ -749,7 +749,7 @@ static bool __is_vma_write_locked(struct vm_area_struct *vma, int *mm_lock_seq)
  */
 static inline void vma_start_write(struct vm_area_struct *vma)
 {
-	int mm_lock_seq;
+	long mm_lock_seq;
 
 	if (__is_vma_write_locked(vma, &mm_lock_seq))
 		return;
@@ -767,7 +767,7 @@ static inline void vma_start_write(struct vm_area_struct *vma)
 
 static inline void vma_assert_write_locked(struct vm_area_struct *vma)
 {
-	int mm_lock_seq;
+	long mm_lock_seq;
 
 	VM_BUG_ON_VMA(!__is_vma_write_locked(vma, &mm_lock_seq), vma);
 }
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5d8cdebd42bc..0dc57d6cfe38 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -715,7 +715,7 @@ struct vm_area_struct {
 	 * counter reuse can only lead to occasional unnecessary use of the
 	 * slowpath.
 	 */
-	int vm_lock_seq;
+	long vm_lock_seq;
 	/* Unstable RCU readers are allowed to read this. */
 	struct vma_lock *vm_lock;
 #endif
@@ -898,7 +898,7 @@ struct mm_struct {
 		 * Can be read with ACQUIRE semantics if not holding write
 		 * mmap_lock.
 		 */
-		int mm_lock_seq;
+		long mm_lock_seq;
 #endif
 
 
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 9d23635bc701..f8fd6d879aa9 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -105,7 +105,7 @@ static inline void inc_mm_lock_seq(struct mm_struct *mm, bool acquire)
 	}
 }
 
-static inline bool mmap_lock_speculation_start(struct mm_struct *mm, int *seq)
+static inline bool mmap_lock_speculation_start(struct mm_struct *mm, long *seq)
 {
 	/* Pairs with RELEASE semantics in inc_mm_lock_seq(). */
 	*seq = smp_load_acquire(&mm->mm_lock_seq);
@@ -113,7 +113,7 @@ static inline bool mmap_lock_speculation_start(struct mm_struct *mm, int *seq)
 	return (*seq & 1) == 0;
 }
 
-static inline bool mmap_lock_speculation_end(struct mm_struct *mm, int seq)
+static inline bool mmap_lock_speculation_end(struct mm_struct *mm, long seq)
 {
 	/* Pairs with ACQUIRE semantics in inc_mm_lock_seq(). */
 	smp_rmb();
@@ -123,8 +123,8 @@ static inline bool mmap_lock_speculation_end(struct mm_struct *mm, int seq)
 #else
 static inline void init_mm_lock_seq(struct mm_struct *mm) {}
 static inline void inc_mm_lock_seq(struct mm_struct *mm, bool acquire) {}
-static inline bool mmap_lock_speculation_start(struct mm_struct *mm, int *seq) { return false; }
-static inline bool mmap_lock_speculation_end(struct mm_struct *mm, int seq) { return false; }
+static inline bool mmap_lock_speculation_start(struct mm_struct *mm, long *seq) { return false; }
+static inline bool mmap_lock_speculation_end(struct mm_struct *mm, long seq) { return false; }
 #endif
 
 /*
-- 
2.43.5