zfsonlinux/zfs — Issue #469: mounting btrfs FS on zfs zvol hangs
Author: behlendorf
Created: 2011-11-28 19:50:48+00:00
State: open
Labels: Bug, ZVOL

yes, you'll probably think that is crazy, but after observing better performance with btrfs in some work loads on md RAID5 than btrfs builtin RAID10, I thought I'd try btrfs on zfs (in-kernel, not fuse) zvol (on raidz) just for a laugh.

While this procedure worked for ext4 and xfs, for btrfs, the mount hangs suggesting there might be something wrong with btrfs and/or zfs.

Here's what I'm doing:

zpool create X raidz /dev/sd{a,b,c,d,e,f}
zfs create -V 6T -o refreservation=0 X/Y
mkfs.btrfs /dev/zvol/X/Y
mount /dev/zvol/X/Y /mnt

backtrace for mount:

mount D 0000000000000009 0 2193 1761 0x00000000
ffff880401b4d9a8 0000000000000082 0000000000000001 0000000000000000
ffff880401b4dfd8 ffff880401b4dfd8 ffff880401b4dfd8 0000000000012a40
ffff8802092f0000 ffff88040ef7dc80 ffff880401b4d988 ffff88041fa732c0
Call Trace:
[] ? __lock_page+0x70/0x70
[] schedule+0x3f/0x60
[] io_schedule+0x8f/0xd0
[] sleep_on_page+0xe/0x20
[] __wait_on_bit+0x5f/0x90
[] wait_on_page_bit+0x78/0x80
[] ? autoremove_wake_function+0x40/0x40
[] read_extent_buffer_pages+0x3ca/0x430 [btrfs]
[] ? btrfs_destroy_pinned_extent+0xb0/0xb0 [btrfs]
[] btree_read_extent_buffer_pages.isra.62+0x8a/0xc0 [btrfs]
[] read_tree_block+0x41/0x60 [btrfs]
[] open_ctree+0xe75/0x1760 [btrfs]
[] ? snprintf+0x34/0x40
[] btrfs_fill_super.isra.38+0x78/0x150 [btrfs]
[] ? disk_name+0xba/0xc0
[] ? strlcpy+0x47/0x60
[] btrfs_mount+0x3c6/0x470 [btrfs]
[] mount_fs+0x43/0x1b0
[] vfs_kern_mount+0x6a/0xc0
[] do_kern_mount+0x54/0x110
[] do_mount+0x1a4/0x260
[] sys_mount+0x90/0xe0
[] system_call_fastpath+0x16/0x1b

3.0.0-13-generic #22-Ubuntu SMP Wed Nov 2 13:27:26 UTC 2011
x86_64

Best regards,
Stephane