linux-kernel - [PATCHv2 4/4] zram: drop wb_limit

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Message-ID: <20251113085402.1811522-5-senozhatsky@chromium.org>
Date: Thu, 13 Nov 2025 17:54:02 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Yuwen Chen <ywen.chen@...mail.com>,
	Richard Chang <richardycc@...gle.com>
Cc: Brian Geffon <bgeffon@...gle.com>,
	Fengyu Lian <licayy@...look.com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-block@...r.kernel.org,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCHv2 4/4] zram: drop wb_limit_lock

We don't need wb_limit_lock.  Writeback limit setters take an
exclusive write zram init_lock, while wb_limit modifications
happen only from a single task and under zram read init_lock.
No concurrent wb_limit modifications are possible (we permit
only one post-processing task at a time).  Add lockdep
assertions to wb_limit mutators.

While at it, fixup coding styles.

Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 drivers/block/zram/zram_drv.c | 22 +++++-----------------
 drivers/block/zram/zram_drv.h |  1 -
 2 files changed, 5 insertions(+), 18 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 6312b0437618..28afb010307d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -512,9 +512,7 @@ static ssize_t writeback_limit_enable_store(struct device *dev,
 		return ret;
 
 	down_write(&zram->init_lock);
-	spin_lock(&zram->wb_limit_lock);
 	zram->wb_limit_enable = val;
-	spin_unlock(&zram->wb_limit_lock);
 	up_write(&zram->init_lock);
 	ret = len;
 
@@ -529,9 +527,7 @@ static ssize_t writeback_limit_enable_show(struct device *dev,
 	struct zram *zram = dev_to_zram(dev);
 
 	down_read(&zram->init_lock);
-	spin_lock(&zram->wb_limit_lock);
 	val = zram->wb_limit_enable;
-	spin_unlock(&zram->wb_limit_lock);
 	up_read(&zram->init_lock);
 
 	return sysfs_emit(buf, "%d\n", val);
@@ -549,9 +545,7 @@ static ssize_t writeback_limit_store(struct device *dev,
 		return ret;
 
 	down_write(&zram->init_lock);
-	spin_lock(&zram->wb_limit_lock);
 	zram->bd_wb_limit = val;
-	spin_unlock(&zram->wb_limit_lock);
 	up_write(&zram->init_lock);
 	ret = len;
 
@@ -559,15 +553,13 @@ static ssize_t writeback_limit_store(struct device *dev,
 }
 
 static ssize_t writeback_limit_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
+				    struct device_attribute *attr, char *buf)
 {
 	u64 val;
 	struct zram *zram = dev_to_zram(dev);
 
 	down_read(&zram->init_lock);
-	spin_lock(&zram->wb_limit_lock);
 	val = zram->bd_wb_limit;
-	spin_unlock(&zram->wb_limit_lock);
 	up_read(&zram->init_lock);
 
 	return sysfs_emit(buf, "%llu\n", val);
@@ -866,18 +858,18 @@ static struct zram_wb_ctl *init_wb_ctl(struct zram *zram)
 
 static void zram_account_writeback_rollback(struct zram *zram)
 {
-	spin_lock(&zram->wb_limit_lock);
+	lockdep_assert_held_read(&zram->init_lock);
+
 	if (zram->wb_limit_enable)
 		zram->bd_wb_limit +=  1UL << (PAGE_SHIFT - 12);
-	spin_unlock(&zram->wb_limit_lock);
 }
 
 static void zram_account_writeback_submit(struct zram *zram)
 {
-	spin_lock(&zram->wb_limit_lock);
+	lockdep_assert_held_read(&zram->init_lock);
+
 	if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
 		zram->bd_wb_limit -=  1UL << (PAGE_SHIFT - 12);
-	spin_unlock(&zram->wb_limit_lock);
 }
 
 static int zram_writeback_complete(struct zram *zram, struct zram_wb_req *req)
@@ -991,13 +983,10 @@ static int zram_writeback_slots(struct zram *zram,
 
 	blk_start_plug(&wb_ctl->plug);
 	while ((pps = select_pp_slot(ctl))) {
-		spin_lock(&zram->wb_limit_lock);
 		if (zram->wb_limit_enable && !zram->bd_wb_limit) {
-			spin_unlock(&zram->wb_limit_lock);
 			ret = -EIO;
 			break;
 		}
-		spin_unlock(&zram->wb_limit_lock);
 
 		while (!req) {
 			req = select_idle_req(wb_ctl);
@@ -2944,7 +2933,6 @@ static int zram_add(void)
 	init_rwsem(&zram->init_lock);
 #ifdef CONFIG_ZRAM_WRITEBACK
 	zram->wb_batch_size = 1;
-	spin_lock_init(&zram->wb_limit_lock);
 #endif
 
 	/* gendisk structure */
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 1a647f42c1a4..c6d94501376c 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -127,7 +127,6 @@ struct zram {
 	bool claim; /* Protected by disk->open_mutex */
 #ifdef CONFIG_ZRAM_WRITEBACK
 	struct file *backing_dev;
-	spinlock_t wb_limit_lock;
 	bool wb_limit_enable;
 	u32 wb_batch_size;
 	u64 bd_wb_limit;
-- 
2.51.2.1041.gc1ab5b90ca-goog