From 53176dde0acd8fa49c6c2e6097283acc6241480f Mon Sep 17 00:00:00 2001 From: David Sterba Date: Thu, 5 Apr 2018 01:41:06 +0200 Subject: [PATCH] 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 --- fs/btrfs/ctree.h | 2 -- fs/btrfs/dev-replace.c | 16 ---------------- fs/btrfs/dev-replace.h | 1 - fs/btrfs/disk-io.c | 2 -- fs/btrfs/volumes.c | 13 ++++++------- 5 files changed, 6 insertions(+), 28 deletions(-) diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index b4f97120aecd..5fb4cb646c82 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -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; diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c index 316a29278306..a71661f43dec 100644 --- a/fs/btrfs/dev-replace.c +++ b/fs/btrfs/dev-replace.c @@ -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); diff --git a/fs/btrfs/dev-replace.h b/fs/btrfs/dev-replace.h index 27e3bb0cca11..dd1dcb22c1e3 100644 --- a/fs/btrfs/dev-replace.h +++ b/fs/btrfs/dev-replace.h @@ -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 diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index eca66ac52c7a..cbb7cf4a993d 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -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) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 6c806808b6a1..57174d00f74b 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -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); -- 2.30.2