Commit 0b78877a authored Dec 12, 2017 by Qu Wenruo Committed by David Sterba Mar 31, 2018

Revert "btrfs: qgroups: Retry after commit on getting EDQUOT"



This reverts commit 48a89bc4.

The idea to commit transaction and free some space after hitting qgroup
limit is good, although the problem is it can easily cause deadlocks.

One deadlock example is caused by trying to flush data while still
holding it:

Call Trace:
 __schedule+0x49d/0x10f0
 schedule+0xc6/0x290
 schedule_timeout+0x187/0x1c0
 wait_for_completion+0x204/0x3a0
 btrfs_wait_ordered_extents+0xa40/0xaf0 [btrfs]
 qgroup_reserve+0x913/0xa10 [btrfs]
 btrfs_qgroup_reserve_data+0x3ef/0x580 [btrfs]
 btrfs_check_data_free_space+0x96/0xd0 [btrfs]
 __btrfs_buffered_write+0x3ac/0xd40 [btrfs]
 btrfs_file_write_iter+0x62a/0xba0 [btrfs]
 __vfs_write+0x320/0x430
 vfs_write+0x107/0x270
 SyS_write+0xbf/0x150
 do_syscall_64+0x1b0/0x3d0
 entry_SYSCALL64_slow_path+0x25/0x25

Another can be caused by trying to commit one transaction while nesting
with trans handle held by ourselves:

btrfs_start_transaction()
|- btrfs_qgroup_reserve_meta_pertrans()
   |- qgroup_reserve()
      |- btrfs_join_transaction()
      |- btrfs_commit_transaction()

The retry is causing more problems than exppected when limit is enabled.
At least a graceful EDQUOT is way better than deadlock.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 4ee0d883

fs/btrfs/qgroup.c

+0 −23

Original line number	Diff line number	Diff line
		@@ -2406,7 +2406,6 @@ static int qgroup_reserve(struct btrfs_root *root, u64 num_bytes, bool enforce,
		struct btrfs_fs_info *fs_info = root->fs_info;
		u64 ref_root = root->root_key.objectid;
		int ret = 0;
		int retried = 0;
		struct ulist_node *unode;
		struct ulist_iterator uiter;

		@@ -2420,7 +2419,6 @@ static int qgroup_reserve(struct btrfs_root *root, u64 num_bytes, bool enforce,
		capable(CAP_SYS_RESOURCE))
		enforce = false;

		retry:
		spin_lock(&fs_info->qgroup_lock);
		quota_root = fs_info->quota_root;
		if (!quota_root)
		@@ -2447,27 +2445,6 @@ retry:
		qg = unode_aux_to_qgroup(unode);

		if (enforce && !qgroup_check_limits(qg, num_bytes)) {
		/*
		* Commit the tree and retry, since we may have
		* deletions which would free up space.
		*/
		if (!retried && qgroup_rsv_total(qg) > 0) {
		struct btrfs_trans_handle *trans;

		spin_unlock(&fs_info->qgroup_lock);
		ret = btrfs_start_delalloc_inodes(root, 0);
		if (ret)
		return ret;
		btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
		trans = btrfs_join_transaction(root);
		if (IS_ERR(trans))
		return PTR_ERR(trans);
		ret = btrfs_commit_transaction(trans);
		if (ret)
		return ret;
		retried++;
		goto retry;
		}
		ret = -EDQUOT;
		goto out;
		}

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