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>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index b4f9712..5fb4cb6 100644 (file)
--- 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 316a292..a71661f 100644 (file)
--- 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 27e3bb0..dd1dcb2 100644 (file)
--- 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 eca66ac..cbb7cf4 100644 (file)
--- 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 6c80680..57174d0 100644 (file)
--- 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);