[PATCH 0/2] zram: lockmap tweaks

[PATCH 0/2] zram: lockmap tweaks

[Sebastian Andrzej Siewior]

Sergey, this should be a follow up on 
	https://lore.kernel.org/all/akza1qtgHm7zbjMW@google.com/

Could you try if this does what I claimed it does?

Sebastian Andrzej Siewior (2):
  zram: Move lockmap to be per-zram instead per table
  zram: Use a custom key for each zram object.

 drivers/block/zram/zram_drv.c | 26 +++++++++-----------------
 drivers/block/zram/zram_drv.h |  3 ++-
 2 files changed, 11 insertions(+), 18 deletions(-)

-- 
2.53.0

[PATCH 1/2] zram: Move lockmap to be per-zram instead per table

[Sebastian Andrzej Siewior]

The zram object contains an array zram_table_entry. Each one has a
`lock' variable and each has a matching struct lockdep_map. This mimics
a struct mutex.

It uses always the same key for all lockdep_map instances. This makes it
look like the same lock to lockdep. Therefore it could be reduced to
have one lockdep_map per struct zram.

Use only one struct lockdep_map per struct zram.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/block/zram/zram_drv.c | 21 +++++++++------------
 drivers/block/zram/zram_drv.h |  2 +-
 2 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index ace65c586072b..4223002d80b41 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -57,14 +57,12 @@ static size_t huge_class_size;
 static const struct block_device_operations zram_devops;
 
 static void slot_free(struct zram *zram, u32 index);
-#define slot_dep_map(zram, index) (&(zram)->table[(index)].dep_map)
 
-static void slot_lock_init(struct zram *zram, u32 index)
+static void slot_lock_init(struct zram *zram)
 {
 	static struct lock_class_key __key;
 
-	lockdep_init_map(slot_dep_map(zram, index), "zram->table[index].lock",
-			 &__key, 0);
+	lockdep_init_map(&zram->table_lock_map, "zram->table[index].lock", &__key, 0);
 }
 
 /*
@@ -84,8 +82,8 @@ static __must_check bool slot_trylock(struct zram *zram, u32 index)
 	unsigned long *lock = &zram->table[index].__lock;
 
 	if (!test_and_set_bit_lock(ZRAM_ENTRY_LOCK, lock)) {
-		mutex_acquire(slot_dep_map(zram, index), 0, 1, _RET_IP_);
-		lock_acquired(slot_dep_map(zram, index), _RET_IP_);
+		mutex_acquire(&zram->table_lock_map, 0, 1, _RET_IP_);
+		lock_acquired(&zram->table_lock_map, _RET_IP_);
 		return true;
 	}
 
@@ -96,16 +94,16 @@ static void slot_lock(struct zram *zram, u32 index)
 {
 	unsigned long *lock = &zram->table[index].__lock;
 
-	mutex_acquire(slot_dep_map(zram, index), 0, 0, _RET_IP_);
+	mutex_acquire(&zram->table_lock_map, 0, 0, _RET_IP_);
 	wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK, TASK_UNINTERRUPTIBLE);
-	lock_acquired(slot_dep_map(zram, index), _RET_IP_);
+	lock_acquired(&zram->table_lock_map, _RET_IP_);
 }
 
 static void slot_unlock(struct zram *zram, u32 index)
 {
 	unsigned long *lock = &zram->table[index].__lock;
 
-	mutex_release(slot_dep_map(zram, index), _RET_IP_);
+	mutex_release(&zram->table_lock_map, _RET_IP_);
 	clear_and_wake_up_bit(ZRAM_ENTRY_LOCK, lock);
 }
 
@@ -1984,7 +1982,7 @@ static void zram_meta_free(struct zram *zram, u64 disksize)
 
 static bool zram_meta_alloc(struct zram *zram, u64 disksize)
 {
-	size_t num_pages, index;
+	size_t num_pages;
 
 	num_pages = disksize >> PAGE_SHIFT;
 	zram->table = vzalloc(array_size(num_pages, sizeof(*zram->table)));
@@ -2001,8 +1999,7 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
 	if (!huge_class_size)
 		huge_class_size = zs_huge_class_size(zram->mem_pool);
 
-	for (index = 0; index < num_pages; index++)
-		slot_lock_init(zram, index);
+	slot_lock_init(zram);
 
 	return true;
 }
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 08d1774c15db6..8290dc6e23352 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -74,7 +74,6 @@ struct zram_table_entry {
 #endif
 		} attr;
 	};
-	struct lockdep_map dep_map;
 };
 
 struct zram_stats {
@@ -107,6 +106,7 @@ struct zram_stats {
 
 struct zram {
 	struct zram_table_entry *table;
+	struct lockdep_map table_lock_map;
 	struct zs_pool *mem_pool;
 	struct zcomp *comps[ZRAM_MAX_COMPS];
 	struct zcomp_params params[ZRAM_MAX_COMPS];
-- 
2.53.0

[PATCH 2/2] zram: Use a custom key for each zram object.

[Sebastian Andrzej Siewior]

Each struct zram uses the same key for its struct lockdep_map which is
used for locking analysis.
According to Sergey the lock chains might be different if zram1 is used
for and zram2 is for ext4. This might lead to false dead lock reports if
it mixes a zram1 chain with a zram2. This can be avoided if each lockmap
gets its own unique key.c

Use a dynamic lock_class_key for the table_lock_map.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/block/zram/zram_drv.c | 11 +++--------
 drivers/block/zram/zram_drv.h |  1 +
 2 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 4223002d80b41..4bfe63a5225d8 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -58,13 +58,6 @@ static const struct block_device_operations zram_devops;
 
 static void slot_free(struct zram *zram, u32 index);
 
-static void slot_lock_init(struct zram *zram)
-{
-	static struct lock_class_key __key;
-
-	lockdep_init_map(&zram->table_lock_map, "zram->table[index].lock", &__key, 0);
-}
-
 /*
  * entry locking rules:
  *
@@ -1978,6 +1971,7 @@ static void zram_meta_free(struct zram *zram, u64 disksize)
 	zs_destroy_pool(zram->mem_pool);
 	vfree(zram->table);
 	zram->table = NULL;
+	lockdep_unregister_key(&zram->table_lock_key);
 }
 
 static bool zram_meta_alloc(struct zram *zram, u64 disksize)
@@ -1999,7 +1993,8 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
 	if (!huge_class_size)
 		huge_class_size = zs_huge_class_size(zram->mem_pool);
 
-	slot_lock_init(zram);
+	lockdep_register_key(&zram->table_lock_key);
+	lockdep_init_map(&zram->table_lock_map, "zram->table[index].lock", &zram->table_lock_key, 0);
 
 	return true;
 }
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 8290dc6e23352..4fddc582f3b82 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -107,6 +107,7 @@ struct zram_stats {
 struct zram {
 	struct zram_table_entry *table;
 	struct lockdep_map table_lock_map;
+	struct lock_class_key table_lock_key;
 	struct zs_pool *mem_pool;
 	struct zcomp *comps[ZRAM_MAX_COMPS];
 	struct zcomp_params params[ZRAM_MAX_COMPS];
-- 
2.53.0