btrfs: Fix out-of-space bug

Btrfs will report NO_SPACE when we create and remove files for several times,
and we can't write to filesystem until mount it again.

Steps to reproduce:
 1: Create a single-dev btrfs fs with default option
 2: Write a file into it to take up most fs space
 3: Delete above file
 4: Wait about 100s to let chunk removed
 5: goto 2

Script is like following:
 #!/bin/bash

 # Recommend 1.2G space, too large disk will make test slow
 DEV="/dev/sda16"
 MNT="/mnt/tmp"

 dev_size="$(lsblk -bn -o SIZE "$DEV")" || exit 2
 file_size_m=$((dev_size * 75 / 100 / 1024 / 1024))

 echo "Loop write ${file_size_m}M file on $((dev_size / 1024 / 1024))M dev"

 for ((i = 0; i < 10; i++)); do umount "$MNT" 2>/dev/null; done
 echo "mkfs $DEV"
 mkfs.btrfs -f "$DEV" >/dev/null || exit 2
 echo "mount $DEV $MNT"
 mount "$DEV" "$MNT" || exit 2

 for ((loop_i = 0; loop_i < 20; loop_i++)); do
     echo
     echo "loop $loop_i"

     echo "dd file..."
     cmd=(dd if=/dev/zero of="$MNT"/file0 bs=1M count="$file_size_m")
     "${cmd[@]}" 2>/dev/null || {
         # NO_SPACE error triggered
         echo "dd failed: ${cmd[*]}"
         exit 1
     }

     echo "rm file..."
     rm -f "$MNT"/file0 || exit 2

     for ((i = 0; i < 10; i++)); do
         df "$MNT" | tail -1
         sleep 10
     done
 done

Reason:
 It is triggered by commit: 47ab2a6c689913db23ccae38349714edf8365e0a
 which is used to remove empty block groups automatically, but the
 reason is not in that patch. Code before works well because btrfs
 don't need to create and delete chunks so many times with high
 complexity.
 Above bug is caused by many reason, any of them can trigger it.

Reason1:
 When we remove some continuous chunks but leave other chunks after,
 these disk space should be used by chunk-recreating, but in current
 code, only first create will successed.
 Fixed by Forrest Liu <forrestl@synology.com> in:
 Btrfs: fix find_free_dev_extent() malfunction in case device tree has hole

Reason2:
 contains_pending_extent() return wrong value in calculation.
 Fixed by Forrest Liu <forrestl@synology.com> in:
 Btrfs: fix find_free_dev_extent() malfunction in case device tree has hole

Reason3:
 btrfs_check_data_free_space() try to commit transaction and retry
 allocating chunk when the first allocating failed, but space_info->full
 is set in first allocating, and prevent second allocating in retry.
 Fixed in this patch by clear space_info->full in commit transaction.

 Tested for severial times by above script.

Changelog v3->v4:
 use light weight int instead of atomic_t to record have_remove_bgs in
 transaction, suggested by:
 Josef Bacik <jbacik@fb.com>

Changelog v2->v3:
 v2 fixed the bug by adding more commit-transaction, but we
 only need to reclaim space when we are really have no space for
 new chunk, noticed by:
 Filipe David Manana <fdmanana@gmail.com>

 Actually, our code already have this type of commit-and-retry,
 we only need to make it working with removed-bgs.
 v3 fixed the bug with above way.

Changelog v1->v2:
 v1 will introduce a new bug when delete and create chunk in same disk
 space in same transaction, noticed by:
 Filipe David Manana <fdmanana@gmail.com>
 V2 fix this bug by commit transaction after remove block grops.

Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Suggested-by: Filipe David Manana <fdmanana@gmail.com>
Suggested-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/transaction.c

@@ -220,6 +220,7 @@ loop:
 	 * commit the transaction.
 	 */
 	atomic_set(&cur_trans->use_count, 2);
+	cur_trans->have_free_bgs = 0;
 	cur_trans->start_time = get_seconds();
 
 	cur_trans->delayed_refs.href_root = RB_ROOT;
@@ -2037,6 +2038,9 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
 	btrfs_finish_extent_commit(trans, root);
 
+	if (cur_trans->have_free_bgs)
+		btrfs_clear_space_info_full(root->fs_info);
+
 	root->fs_info->last_trans_committed = cur_trans->transid;
 	/*
 	 * We needn't acquire the lock here because there is no other task

fs/btrfs/transaction.h

@@ -47,6 +47,11 @@ struct btrfs_transaction {
 	atomic_t num_writers;
 	atomic_t use_count;
 
+	/*
+	 * true if there is free bgs operations in this transaction
+	 */
+	int have_free_bgs;
+
 	/* Be protected by fs_info->trans_lock when we want to change it. */
 	enum btrfs_trans_state state;
 	struct list_head list;

fs/btrfs/volumes.c

@@ -1310,6 +1310,8 @@ again:
 	if (ret) {
 		btrfs_error(root->fs_info, ret,
 			    "Failed to remove dev extent item");
+	} else {
+		trans->transaction->have_free_bgs = 1;
 	}
 out:
 	btrfs_free_path(path);