Commit 0320b353 authored by Naohiro Aota's avatar Naohiro Aota Committed by David Sterba
Browse files

btrfs: assert that relocation is protected with sb_start_write() 



Relocation of a data block group creates ordered extents. They can cause
a hang when a process is trying to thaw the filesystem.

We should have called sb_start_write(), so the filesystem is not being
frozen. Add an ASSERT to check it is protected.

Reviewed-by: default avatarFilipe Manana <fdmanana@suse.com>
Signed-off-by: default avatarNaohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 7f8d12ea

fs/btrfs/relocation.c

+11 −0
Original line number Diff line number Diff line
@@ -3978,6 +3978,17 @@ int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start) 
	if (!bg)

		return -ENOENT;



	/*

	 * Relocation of a data block group creates ordered extents.  Without

	 * sb_start_write(), we can freeze the filesystem while unfinished

	 * ordered extents are left. Such ordered extents can cause a deadlock

	 * e.g. when syncfs() is waiting for their completion but they can't

	 * finish because they block when joining a transaction, due to the

	 * fact that the freeze locks are being held in write mode.

	 */

	if (bg->flags & BTRFS_BLOCK_GROUP_DATA)

		ASSERT(sb_write_started(fs_info->sb));



	if (btrfs_pinned_by_swapfile(fs_info, bg)) {

		btrfs_put_block_group(bg);

		return -ETXTBSY;