btrfs: extend locking to all space_info members accesses

bytes_pinned is always accessed under space_info->lock, except in
btrfs_preempt_reclaim_metadata_space, however the other members are
accessed under that lock. The reserved member of the rsv's are also
partially accessed under a lock and partially not. Move all these
accesses into the same lock to ensure consistency.

This could potentially race and lead to a flush instead of a commit but
it's not a big problem as it's only for preemptive flush.

CC: stable@vger.kernel.org # 5.15+
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Niels Dossche <niels.dossche@ugent.be>
Signed-off-by: Niels Dossche <dossche.niels@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/space-info.c

@@ -1061,7 +1061,6 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
 			trans_rsv->reserved;
 		if (block_rsv_size < space_info->bytes_may_use)
 			delalloc_size = space_info->bytes_may_use - block_rsv_size;
-		spin_unlock(&space_info->lock);
 
 		/*
 		 * We don't want to include the global_rsv in our calculation,
@@ -1092,6 +1091,8 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
 			flush = FLUSH_DELAYED_REFS_NR;
 		}
 
+		spin_unlock(&space_info->lock);
+
 		/*
 		 * We don't want to reclaim everything, just a portion, so scale
 		 * down the to_reclaim by 1/4.  If it takes us down to 0,