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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: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2018-04-05 01:41:06 +02:00
parent 129827e300
commit 53176dde0a
5 changed files with 6 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/btrfs/ctree.h
View File

@ -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;

16
fs/btrfs/dev-replace.c
View File

@ -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);

1
fs/btrfs/dev-replace.h
View File

@ -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

2
fs/btrfs/disk-io.c
View File

@ -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)

13
fs/btrfs/volumes.c
View File

@ -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);