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Commit 53176dde authored by David Sterba's avatar David Sterba
Browse files

btrfs: dev-replace: remove custom read/write blocking scheme 



After the rw semaphore has been added, the custom blocking using
::blocking_readers and ::read_lock_wq is redundant.

The blocking logic in __btrfs_map_block is replaced by extending the
time the semaphore is held, that has the same blocking effect on writes
as the previous custom scheme that waited until ::blocking_readers was
zero.

Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 129827e3

fs/btrfs/ctree.h

+0 −2
Original line number Diff line number Diff line
@@ -379,8 +379,6 @@ struct btrfs_dev_replace { 


	struct mutex lock_finishing_cancel_unmount;

	struct rw_semaphore rwsem;

	atomic_t blocking_readers;

	wait_queue_head_t read_lock_wq;



	struct btrfs_scrub_progress scrub_progress;

fs/btrfs/dev-replace.c

+0 −16
Original line number Diff line number Diff line
@@ -1012,14 +1012,7 @@ void btrfs_dev_replace_read_unlock(struct btrfs_dev_replace *dev_replace) 


void btrfs_dev_replace_write_lock(struct btrfs_dev_replace *dev_replace)

{

again:

	wait_event(dev_replace->read_lock_wq,

		   atomic_read(&dev_replace->blocking_readers) == 0);

	down_write(&dev_replace->rwsem);

	if (atomic_read(&dev_replace->blocking_readers)) {

		up_write(&dev_replace->rwsem);

		goto again;

	}

}



void btrfs_dev_replace_write_unlock(struct btrfs_dev_replace *dev_replace)
@@ -1027,15 +1020,6 @@ void btrfs_dev_replace_write_unlock(struct btrfs_dev_replace *dev_replace) 
	up_write(&dev_replace->rwsem);

}



/* inc blocking cnt and release read lock */

void btrfs_dev_replace_set_lock_blocking(

					struct btrfs_dev_replace *dev_replace)

{

	/* only set blocking for read lock */

	atomic_inc(&dev_replace->blocking_readers);

	up_read(&dev_replace->rwsem);

}



void btrfs_bio_counter_inc_noblocked(struct btrfs_fs_info *fs_info)

{

	percpu_counter_inc(&fs_info->dev_replace.bio_counter);

fs/btrfs/dev-replace.h

+0 −1
Original line number Diff line number Diff line
@@ -23,6 +23,5 @@ void btrfs_dev_replace_read_lock(struct btrfs_dev_replace *dev_replace); 
void btrfs_dev_replace_read_unlock(struct btrfs_dev_replace *dev_replace);

void btrfs_dev_replace_write_lock(struct btrfs_dev_replace *dev_replace);

void btrfs_dev_replace_write_unlock(struct btrfs_dev_replace *dev_replace);

void btrfs_dev_replace_set_lock_blocking(struct btrfs_dev_replace *dev_replace);



#endif

fs/btrfs/disk-io.c

+0 −2
Original line number Diff line number Diff line
@@ -2142,9 +2142,7 @@ static void btrfs_init_dev_replace_locks(struct btrfs_fs_info *fs_info) 
{

	mutex_init(&fs_info->dev_replace.lock_finishing_cancel_unmount);

	init_rwsem(&fs_info->dev_replace.rwsem);

	atomic_set(&fs_info->dev_replace.blocking_readers, 0);

	init_waitqueue_head(&fs_info->dev_replace.replace_wait);

	init_waitqueue_head(&fs_info->dev_replace.read_lock_wq);

}



static void btrfs_init_qgroup(struct btrfs_fs_info *fs_info)

fs/btrfs/volumes.c

+6 −7
Original line number Diff line number Diff line
@@ -6145,10 +6145,12 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, 


	btrfs_dev_replace_read_lock(dev_replace);

	dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(dev_replace);

	/*

	 * Hold the semaphore for read during the whole operation, write is

	 * requested at commit time but must wait.

	 */

	if (!dev_replace_is_ongoing)

		btrfs_dev_replace_read_unlock(dev_replace);

	else

		btrfs_dev_replace_set_lock_blocking(dev_replace);



	if (dev_replace_is_ongoing && mirror_num == map->num_stripes + 1 &&

	    !need_full_stripe(op) && dev_replace->tgtdev != NULL) {
@@ -6343,11 +6345,8 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, 
	}

out:

	if (dev_replace_is_ongoing) {

		ASSERT(atomic_read(&dev_replace->blocking_readers) > 0);

		btrfs_dev_replace_read_lock(dev_replace);

		/* Barrier implied by atomic_dec_and_test */

		if (atomic_dec_and_test(&dev_replace->blocking_readers))

			cond_wake_up_nomb(&dev_replace->read_lock_wq);

		lockdep_assert_held(&dev_replace->rwsem);

		/* Unlock and let waiting writers proceed */

		btrfs_dev_replace_read_unlock(dev_replace);

	}

	free_extent_map(em);