linux-kernel - [PATCH v2 1/3] zram: Replace bit spinlocks with a spinlock

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Message-ID: <20240620153556.777272-2-bigeasy@linutronix.de>
Date: Thu, 20 Jun 2024 17:28:50 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Minchan Kim <minchan@...nel.org>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Jens Axboe <axboe@...nel.dk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH v2 1/3] zram: Replace bit spinlocks with a spinlock_t.

From: Mike Galbraith <umgwanakikbuti@...il.com>

The bit spinlock disables preemption. The spinlock_t lock becomes a sleeping
lock on PREEMPT_RT and it can not be acquired in this context. In this locked
section, zs_free() acquires a zs_pool::lock, and there is access to
zram::wb_limit_lock.

Add a spinlock_t for locking. Keep the set/ clear ZRAM_LOCK bit after
the lock has been acquired/ dropped. The size of struct zram_table_entry
increases by 4 bytes due to lock and additional 4 bytes padding with
CONFIG_ZRAM_TRACK_ENTRY_ACTIME enabled.

Signed-off-by: Mike Galbraith <umgwanakikbuti@...il.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 drivers/block/zram/zram_drv.c | 22 +++++++++++++++++++---
 drivers/block/zram/zram_drv.h |  1 +
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 3acd7006ad2cc..036845cd4f25e 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -57,19 +57,34 @@ static void zram_free_page(struct zram *zram, size_t index);
 static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 			  struct bio *parent);
 
+static void zram_meta_init_table_locks(struct zram *zram, size_t num_pages)
+{
+	size_t index;
+
+	for (index = 0; index < num_pages; index++)
+		spin_lock_init(&zram->table[index].lock);
+}
+
 static int zram_slot_trylock(struct zram *zram, u32 index)
 {
-	return bit_spin_trylock(ZRAM_LOCK, &zram->table[index].flags);
+	int ret;
+
+	ret = spin_trylock(&zram->table[index].lock);
+	if (ret)
+		__set_bit(ZRAM_LOCK, &zram->table[index].flags);
+	return ret;
 }
 
 static void zram_slot_lock(struct zram *zram, u32 index)
 {
-	bit_spin_lock(ZRAM_LOCK, &zram->table[index].flags);
+	spin_lock(&zram->table[index].lock);
+	__set_bit(ZRAM_LOCK, &zram->table[index].flags);
 }
 
 static void zram_slot_unlock(struct zram *zram, u32 index)
 {
-	bit_spin_unlock(ZRAM_LOCK, &zram->table[index].flags);
+	__clear_bit(ZRAM_LOCK, &zram->table[index].flags);
+	spin_unlock(&zram->table[index].lock);
 }
 
 static inline bool init_done(struct zram *zram)
@@ -1226,6 +1241,7 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
 
 	if (!huge_class_size)
 		huge_class_size = zs_huge_class_size(zram->mem_pool);
+	zram_meta_init_table_locks(zram, num_pages);
 	return true;
 }
 
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 35e3221446292..dcc3c106ce713 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -69,6 +69,7 @@ struct zram_table_entry {
 		unsigned long element;
 	};
 	unsigned long flags;
+	spinlock_t lock;
 #ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME
 	ktime_t ac_time;
 #endif
-- 
2.45.2