[dm-devel] [PATCH 2/4] dm-bufio: change mutex to rw_semaphore

[Mikulas Patocka]

Change mutex to rw_semaphore, so that there could be multiple processes
inside dm_bufio_lock_read/dm_bufio_unlock_read concurrently.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>

---
 drivers/md/dm-bufio.c |   16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

Index: linux-2.6/drivers/md/dm-bufio.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-bufio.c	2022-10-10 11:13:57.000000000 +0200
+++ linux-2.6/drivers/md/dm-bufio.c	2022-10-10 11:13:57.000000000 +0200
@@ -81,7 +81,7 @@
  *	context.
  */
 struct dm_bufio_client {
-	struct mutex lock;
+	struct rw_semaphore lock;
 	spinlock_t spinlock;
 	bool no_sleep;
 
@@ -174,7 +174,7 @@ static void dm_bufio_lock(struct dm_bufi
 	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
 		spin_lock_bh(&c->spinlock);
 	else
-		mutex_lock_nested(&c->lock, dm_bufio_in_request());
+		down_write_nested(&c->lock, dm_bufio_in_request());
 }
 
 static int dm_bufio_trylock(struct dm_bufio_client *c)
@@ -182,7 +182,7 @@ static int dm_bufio_trylock(struct dm_bu
 	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
 		return spin_trylock_bh(&c->spinlock);
 	else
-		return mutex_trylock(&c->lock);
+		return down_write_trylock(&c->lock);
 }
 
 static void dm_bufio_unlock(struct dm_bufio_client *c)
@@ -190,18 +190,18 @@ static void dm_bufio_unlock(struct dm_bu
 	if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
 		spin_unlock_bh(&c->spinlock);
 	else
-		mutex_unlock(&c->lock);
+		up_write(&c->lock);
 }
 
 void dm_bufio_lock_read(struct dm_bufio_client *c)
 {
-	mutex_lock(&c->lock);
+	down_read(&c->lock);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_lock_read);
 
 void dm_bufio_unlock_read(struct dm_bufio_client *c)
 {
-	mutex_unlock(&c->lock);
+	up_read(&c->lock);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_unlock_read);
 
@@ -1808,7 +1808,7 @@ struct dm_bufio_client *dm_bufio_client_
 		c->n_buffers[i] = 0;
 	}
 
-	mutex_init(&c->lock);
+	init_rwsem(&c->lock);
 	spin_lock_init(&c->spinlock);
 	INIT_LIST_HEAD(&c->reserved_buffers);
 	c->need_reserved_buffers = reserved_buffers;
@@ -1887,7 +1887,6 @@ bad:
 	kmem_cache_destroy(c->slab_buffer);
 	dm_io_client_destroy(c->dm_io);
 bad_dm_io:
-	mutex_destroy(&c->lock);
 	kfree(c);
 bad_client:
 	return ERR_PTR(r);
@@ -1935,7 +1934,6 @@ void dm_bufio_client_destroy(struct dm_b
 	kmem_cache_destroy(c->slab_cache);
 	kmem_cache_destroy(c->slab_buffer);
 	dm_io_client_destroy(c->dm_io);
-	mutex_destroy(&c->lock);
 	if (c->no_sleep)
 		static_branch_dec(&no_sleep_enabled);
 	kfree(c);