zram: Replace bit spinlocks with a spinlock_t.

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@gmail.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20240906141520.730009-2-bigeasy@linutronix.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/zram/zram_drv.c

@@ -59,17 +59,24 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 
 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)
@@ -1211,7 +1218,7 @@ static void zram_meta_free(struct zram *zram, u64 disksize)
 
 static bool zram_meta_alloc(struct zram *zram, u64 disksize)
 {
-	size_t num_pages;
+	size_t num_pages, index;
 
 	num_pages = disksize >> PAGE_SHIFT;
 	zram->table = vzalloc(array_size(num_pages, sizeof(*zram->table)));
@@ -1226,6 +1233,9 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
 
 	if (!huge_class_size)
 		huge_class_size = zs_huge_class_size(zram->mem_pool);
+
+	for (index = 0; index < num_pages; index++)
+		spin_lock_init(&zram->table[index].lock);
 	return true;
 }
 

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