linux-kernel - [PATCH v2 tip/perf/core 2/5] mm: switch to 64-bit mm_lock_seq/vm_lock

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Message-ID: <20241001225207.2215639-3-andrii@kernel.org>
Date: Tue,  1 Oct 2024 15:52:04 -0700
From: Andrii Nakryiko <andrii@...nel.org>
To: linux-trace-kernel@...r.kernel.org,
	peterz@...radead.org,
	oleg@...hat.com
Cc: rostedt@...dmis.org,
	mhiramat@...nel.org,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	jolsa@...nel.org,
	paulmck@...nel.org,
	willy@...radead.org,
	surenb@...gle.com,
	akpm@...ux-foundation.org,
	linux-mm@...ck.org,
	mjguzik@...il.com,
	brauner@...nel.org,
	jannh@...gle.com,
	mhocko@...nel.org,
	vbabka@...e.cz,
	mingo@...nel.org,
	Andrii Nakryiko <andrii@...nel.org>
Subject: [PATCH v2 tip/perf/core 2/5] mm: switch to 64-bit mm_lock_seq/vm_lock_seq on 64-bit architectures

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@...gle.com>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
---
 include/linux/mm.h        | 6 +++---
 include/linux/mm_types.h  | 4 ++--
 include/linux/mmap_lock.h | 4 ++--
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6549d0979b28..f8e75d0642a8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -716,7 +716,7 @@ 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);
 
@@ -735,7 +735,7 @@ 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;
@@ -753,7 +753,7 @@ 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 d5e3f907eea4..c045543f43d9 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -705,7 +705,7 @@ struct vm_area_struct {
 	 * counter reuse can only lead to occasional unnecessary use of the
 	 * slowpath.
 	 */
-	int vm_lock_seq;
+	long vm_lock_seq;
 	struct vma_lock *vm_lock;
 #endif
 
@@ -887,7 +887,7 @@ 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..fca527dece63 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();
-- 
2.43.5