linux-kernel - Re: [PATCHv4 14/17] zsmalloc: make zspage lock preemptible

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Message-ID: <c5bpvju3ulaylrhkqieqljezke6xejv6ycrkgarn2ufrnzelzm@4rs2r6qm6xmm>
Date: Mon, 3 Feb 2025 13:56:05 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 14/17] zsmalloc: make zspage lock preemptible

On (25/02/03 12:13), Sergey Senozhatsky wrote:
> > Just my 2c.
> 
> Perhaps we can sprinkle some lockdep on it.

I forgot to rwsem_release() in zspage_write_unlock() and that
has triggered lockdep :)

---
 mm/zsmalloc.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 956445f4d554..1d4700e457d4 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -308,6 +308,10 @@ struct zspage {
 	struct list_head list; /* fullness list */
 	struct zs_pool *pool;
 	atomic_t lock;
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map lockdep_map;
+#endif
 };
 
 struct mapping_area {
@@ -319,6 +323,12 @@ struct mapping_area {
 
 static void zspage_lock_init(struct zspage *zspage)
 {
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	static struct lock_class_key key;
+
+	lockdep_init_map(&zspage->lockdep_map, "zsmalloc-page", &key, 0);
+#endif
+
 	atomic_set(&zspage->lock, ZS_PAGE_UNLOCKED);
 }
 
@@ -344,11 +354,19 @@ static void zspage_read_lock(struct zspage *zspage)
 			continue;
 		}
 	} while (!atomic_try_cmpxchg(lock, &old, old + 1));
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	rwsem_acquire_read(&zspage->lockdep_map, 0, 0, _RET_IP_);
+#endif
 }
 
 static void zspage_read_unlock(struct zspage *zspage)
 {
 	atomic_dec(&zspage->lock);
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	rwsem_release(&zspage->lockdep_map, _RET_IP_);
+#endif
 }
 
 static bool zspage_try_write_lock(struct zspage *zspage)
@@ -357,8 +375,12 @@ static bool zspage_try_write_lock(struct zspage *zspage)
 	int old = ZS_PAGE_UNLOCKED;
 
 	preempt_disable();
-	if (atomic_try_cmpxchg(lock, &old, ZS_PAGE_WRLOCKED))
+	if (atomic_try_cmpxchg(lock, &old, ZS_PAGE_WRLOCKED)) {
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+		rwsem_acquire(&zspage->lockdep_map, 0, 0, _RET_IP_);
+#endif
 		return true;
+	}
 
 	preempt_enable();
 	return false;
@@ -367,6 +389,9 @@ static bool zspage_try_write_lock(struct zspage *zspage)
 static void zspage_write_unlock(struct zspage *zspage)
 {
 	atomic_set(&zspage->lock, ZS_PAGE_UNLOCKED);
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	rwsem_release(&zspage->lockdep_map, _RET_IP_);
+#endif
 	preempt_enable();
 }
 
-- 
2.48.1.362.g079036d154-goog