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

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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
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13
fs/btrfs/volumes.c
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@@ -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);