Commit 15d1ff81 authored by Liu Bo's avatar Liu Bo Committed by Chris Mason
Browse files

Btrfs: fix deadlock during allocating chunks 



This deadlock comes from xfstests 251.

We'll hold the chunk_mutex throughout the whole of a chunk allocation.
But if we find that we've used up system chunk space, we need to allocate a
new system chunk, but this will lead to a recursion of chunk allocation and end
up with a deadlock on chunk_mutex.
So instead we need to allocate the system chunk first if we find we're in ENOSPC.

Signed-off-by: default avatarLiu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 2bcc0328

fs/btrfs/extent-tree.c

+50 −0
Original line number Diff line number Diff line
@@ -3445,6 +3445,50 @@ static int should_alloc_chunk(struct btrfs_root *root, 
	return 1;

}



static u64 get_system_chunk_thresh(struct btrfs_root *root, u64 type)

{

	u64 num_dev;



	if (type & BTRFS_BLOCK_GROUP_RAID10 ||

	    type & BTRFS_BLOCK_GROUP_RAID0)

		num_dev = root->fs_info->fs_devices->rw_devices;

	else if (type & BTRFS_BLOCK_GROUP_RAID1)

		num_dev = 2;

	else

		num_dev = 1;	/* DUP or single */



	/* metadata for updaing devices and chunk tree */

	return btrfs_calc_trans_metadata_size(root, num_dev + 1);

}



static void check_system_chunk(struct btrfs_trans_handle *trans,

			       struct btrfs_root *root, u64 type)

{

	struct btrfs_space_info *info;

	u64 left;

	u64 thresh;



	info = __find_space_info(root->fs_info, BTRFS_BLOCK_GROUP_SYSTEM);

	spin_lock(&info->lock);

	left = info->total_bytes - info->bytes_used - info->bytes_pinned -

		info->bytes_reserved - info->bytes_readonly;

	spin_unlock(&info->lock);



	thresh = get_system_chunk_thresh(root, type);

	if (left < thresh && btrfs_test_opt(root, ENOSPC_DEBUG)) {

		printk(KERN_INFO "left=%llu, need=%llu, flags=%llu\n",

		       left, thresh, type);

		dump_space_info(info, 0, 0);

	}



	if (left < thresh) {

		u64 flags;



		flags = btrfs_get_alloc_profile(root->fs_info->chunk_root, 0);

		btrfs_alloc_chunk(trans, root, flags);

	}

}



static int do_chunk_alloc(struct btrfs_trans_handle *trans,

			  struct btrfs_root *extent_root, u64 alloc_bytes,

			  u64 flags, int force)
@@ -3515,6 +3559,12 @@ again: 
			force_metadata_allocation(fs_info);

	}



	/*

	 * Check if we have enough space in SYSTEM chunk because we may need

	 * to update devices.

	 */

	check_system_chunk(trans, extent_root, flags);



	ret = btrfs_alloc_chunk(trans, extent_root, flags);

	if (ret < 0 && ret != -ENOSPC)

		goto out;

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