Commit 06297d8c authored by David Sterba's avatar David Sterba
Browse files

btrfs: switch extent_buffer blocking_writers from atomic to int 



The blocking_writers is either 0 or 1 and always updated under the lock,
so we don't need the atomic_t semantics.

Reviewed-by: default avatarNikolay Borisov <nborisov@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 38e9372e

fs/btrfs/extent_io.c

+1 −1
Original line number Diff line number Diff line
@@ -4857,7 +4857,7 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start, 
	eb->bflags = 0;

	rwlock_init(&eb->lock);

	atomic_set(&eb->blocking_readers, 0);

	atomic_set(&eb->blocking_writers, 0);

	eb->blocking_writers = 0;

	eb->lock_nested = false;

	init_waitqueue_head(&eb->write_lock_wq);

	init_waitqueue_head(&eb->read_lock_wq);

fs/btrfs/extent_io.h

+1 −1
Original line number Diff line number Diff line
@@ -167,7 +167,7 @@ struct extent_buffer { 
	struct rcu_head rcu_head;

	pid_t lock_owner;



	atomic_t blocking_writers;

	int blocking_writers;

	atomic_t blocking_readers;

	bool lock_nested;

	/* >= 0 if eb belongs to a log tree, -1 otherwise */

fs/btrfs/locking.c

+20 −26
Original line number Diff line number Diff line
@@ -111,10 +111,10 @@ void btrfs_set_lock_blocking_write(struct extent_buffer *eb) 
	 */

	if (eb->lock_nested && current->pid == eb->lock_owner)

		return;

	if (atomic_read(&eb->blocking_writers) == 0) {

	if (eb->blocking_writers == 0) {

		btrfs_assert_spinning_writers_put(eb);

		btrfs_assert_tree_locked(eb);

		atomic_inc(&eb->blocking_writers);

		eb->blocking_writers++;

		write_unlock(&eb->lock);

	}

}
@@ -148,12 +148,11 @@ void btrfs_clear_lock_blocking_write(struct extent_buffer *eb) 
	 */

	if (eb->lock_nested && current->pid == eb->lock_owner)

		return;

	BUG_ON(atomic_read(&eb->blocking_writers) != 1);

	write_lock(&eb->lock);

	BUG_ON(eb->blocking_writers != 1);

	btrfs_assert_spinning_writers_get(eb);

	/* atomic_dec_and_test implies a barrier */

	if (atomic_dec_and_test(&eb->blocking_writers))

		cond_wake_up_nomb(&eb->write_lock_wq);

	if (--eb->blocking_writers == 0)

		cond_wake_up(&eb->write_lock_wq);

}



/*
@@ -167,12 +166,10 @@ void btrfs_tree_read_lock(struct extent_buffer *eb) 
	if (trace_btrfs_tree_read_lock_enabled())

		start_ns = ktime_get_ns();

again:

	BUG_ON(!atomic_read(&eb->blocking_writers) &&

	       current->pid == eb->lock_owner);



	read_lock(&eb->lock);

	if (atomic_read(&eb->blocking_writers) &&

	    current->pid == eb->lock_owner) {

	BUG_ON(eb->blocking_writers == 0 &&

	       current->pid == eb->lock_owner);

	if (eb->blocking_writers && current->pid == eb->lock_owner) {

		/*

		 * This extent is already write-locked by our thread. We allow

		 * an additional read lock to be added because it's for the same
@@ -185,10 +182,10 @@ void btrfs_tree_read_lock(struct extent_buffer *eb) 
		trace_btrfs_tree_read_lock(eb, start_ns);

		return;

	}

	if (atomic_read(&eb->blocking_writers)) {

	if (eb->blocking_writers) {

		read_unlock(&eb->lock);

		wait_event(eb->write_lock_wq,

			   atomic_read(&eb->blocking_writers) == 0);

			   eb->blocking_writers == 0);

		goto again;

	}

	btrfs_assert_tree_read_locks_get(eb);
@@ -203,11 +200,11 @@ void btrfs_tree_read_lock(struct extent_buffer *eb) 
 */

int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)

{

	if (atomic_read(&eb->blocking_writers))

	if (eb->blocking_writers)

		return 0;



	read_lock(&eb->lock);

	if (atomic_read(&eb->blocking_writers)) {

	if (eb->blocking_writers) {

		read_unlock(&eb->lock);

		return 0;

	}
@@ -223,13 +220,13 @@ int btrfs_tree_read_lock_atomic(struct extent_buffer *eb) 
 */

int btrfs_try_tree_read_lock(struct extent_buffer *eb)

{

	if (atomic_read(&eb->blocking_writers))

	if (eb->blocking_writers)

		return 0;



	if (!read_trylock(&eb->lock))

		return 0;



	if (atomic_read(&eb->blocking_writers)) {

	if (eb->blocking_writers) {

		read_unlock(&eb->lock);

		return 0;

	}
@@ -245,13 +242,11 @@ int btrfs_try_tree_read_lock(struct extent_buffer *eb) 
 */

int btrfs_try_tree_write_lock(struct extent_buffer *eb)

{

	if (atomic_read(&eb->blocking_writers) ||

	    atomic_read(&eb->blocking_readers))

	if (eb->blocking_writers || atomic_read(&eb->blocking_readers))

		return 0;



	write_lock(&eb->lock);

	if (atomic_read(&eb->blocking_writers) ||

	    atomic_read(&eb->blocking_readers)) {

	if (eb->blocking_writers || atomic_read(&eb->blocking_readers)) {

		write_unlock(&eb->lock);

		return 0;

	}
@@ -322,10 +317,9 @@ void btrfs_tree_lock(struct extent_buffer *eb) 
	WARN_ON(eb->lock_owner == current->pid);

again:

	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);

	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);

	wait_event(eb->write_lock_wq, eb->blocking_writers == 0);

	write_lock(&eb->lock);

	if (atomic_read(&eb->blocking_readers) ||

	    atomic_read(&eb->blocking_writers)) {

	if (atomic_read(&eb->blocking_readers) || eb->blocking_writers) {

		write_unlock(&eb->lock);

		goto again;

	}
@@ -340,7 +334,7 @@ void btrfs_tree_lock(struct extent_buffer *eb) 
 */

void btrfs_tree_unlock(struct extent_buffer *eb)

{

	int blockers = atomic_read(&eb->blocking_writers);

	int blockers = eb->blocking_writers;



	BUG_ON(blockers > 1);
@@ -351,7 +345,7 @@ void btrfs_tree_unlock(struct extent_buffer *eb) 


	if (blockers) {

		btrfs_assert_no_spinning_writers(eb);

		atomic_dec(&eb->blocking_writers);

		eb->blocking_writers--;

		/* Use the lighter barrier after atomic */

		smp_mb__after_atomic();

		cond_wake_up_nomb(&eb->write_lock_wq);

fs/btrfs/print-tree.c

+1 −1
Original line number Diff line number Diff line
@@ -155,7 +155,7 @@ static void print_eb_refs_lock(struct extent_buffer *eb) 
"refs %u lock (w:%d r:%d bw:%d br:%d sw:%d sr:%d) lock_owner %u current %u",

		   atomic_read(&eb->refs), atomic_read(&eb->write_locks),

		   atomic_read(&eb->read_locks),

		   atomic_read(&eb->blocking_writers),

		   eb->blocking_writers,

		   atomic_read(&eb->blocking_readers),

		   atomic_read(&eb->spinning_writers),

		   atomic_read(&eb->spinning_readers),