oops unmounting

[tobydickenson]

Yesterday I had a snapshot that would not unmount. Today, after rebooting, I see there was a logged kernel bug.

This all occurred while setting up a zfs snapshot for a remote backup using rsnapshot.

From memory, the following operations led up to this oops:

1. creating a snapshot with "zfs snapshot -r". I have one filesystem in the pool, tank/files.
2. "zfs snapshot -r" again, and seeing the error message that this snapshot already exists.
3. deleting and recreating the snapshot several times. sometimes using -r, and sometimes deleting the snapshot for tank and tank/files independently.
4. "zfs snapshot -r" after deleting the snapshot for tank/files, but while the snapshot for tank still existed.

There was low read/write activity during this, partly using the kernel nfs server.

Eventually the snapshot could not be unmounted. unmount reported that the filesystem was in use, but lsof did not identify any processes using files.

zfs scrub is clean today, after a reboot.

Ubuntu 11.10 with zfs installed from ppa:

$ dpkg-query -l|grep zfs
ii libzfs1 0.6.0.56-0ubuntu1oneiric1 Native ZFS filesystem library for Linux
ii mountall 2.31-zfs1 filesystem mounting tool
ii ubuntu-zfs 6oneiric Native ZFS filesystem metapackage for Ubuntu.
ii zfs-dkms 0.6.0.56-0ubuntu1oneiric1 Native ZFS filesystem kernel modules for Linux
ii zfsutils 0.6.0.56-0ubuntu1oneiric1 Native ZFS management utilities for Linux

[tobydickenson]

Apr 7 21:37:50 benton kernel: [ 7633.313683] BUG: unable to handle kernel NULL pointer dereference at 0000000000000400
Apr 7 21:37:50 benton kernel: [ 7633.313849] IP: [] zfs_preumount+0x10/0x30 [zfs]
Apr 7 21:37:50 benton kernel: [ 7633.314055] PGD 50e14067 PUD d70c067 PMD 0
Apr 7 21:37:50 benton kernel: [ 7633.314149] Oops: 0000 [#1] SMP
Apr 7 21:37:50 benton kernel: [ 7633.314225] CPU 0
Apr 7 21:37:50 benton kernel: [ 7633.314265] Modules linked in: sp5100_tco nfsd nfs lockd fscache auth_rpcgss nfs_acl sunrpc amd64_edac_mod edac_core ghes hed k10temp edac_mce_amd i2c_piix4 radeon ttm drm_kms_helper drm i2c_algo_bit shpchp jc42 ipmi_si ipmi_msghandler lp parport zfs(P) zcommon(P) znvpair(P) zavl(P) zunicode(P) spl zlib_deflate usb_storage uas usbhid hid tg3 ahci libahci pata_atiixp
Apr 7 21:37:50 benton kernel: [ 7633.315106]
Apr 7 21:37:50 benton kernel: [ 7633.315140] Pid: 2710, comm: mount.zfs Tainted: P 3.0.0-17-server #30-Ubuntu HP ProLiant MicroServer
Apr 7 21:37:50 benton kernel: [ 7633.315331] RIP: 0010:[] [] zfs_preumount+0x10/0x30 [zfs]
Apr 7 21:37:50 benton kernel: [ 7633.315559] RSP: 0018:ffff88000c835d38 EFLAGS: 00010296
Apr 7 21:37:50 benton kernel: [ 7633.315657] RAX: 0000000000000000 RBX: ffff880043a02c00 RCX: 00000000000bc7a9
Apr 7 21:37:50 benton kernel: [ 7633.315785] RDX: 00000000000bc7a8 RSI: 00000000000158a0 RDI: 0000000000000000
Apr 7 21:37:50 benton kernel: [ 7633.315914] RBP: ffff88000c835d38 R08: ffffea00018cdc40 R09: ffffffffa008f9cb
Apr 7 21:37:50 benton kernel: [ 7633.316012] R10: ffff8800351fa800 R11: 0000000000000002 R12: ffffffffa01fe4c0
Apr 7 21:37:50 benton kernel: [ 7633.316012] R13: ffffffffa01d4ae0 R14: ffff88000c835db8 R15: 0000000002000000
Apr 7 21:37:50 benton kernel: [ 7633.316012] FS: 00007fd49ac92c20(0000) GS:ffff880077c00000(0000) knlGS:00000000f75a9b40
Apr 7 21:37:50 benton kernel: [ 7633.316012] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Apr 7 21:37:50 benton kernel: [ 7633.316012] CR2: 0000000000000400 CR3: 0000000034ea0000 CR4: 00000000000006f0
Apr 7 21:37:50 benton kernel: [ 7633.316012] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Apr 7 21:37:50 benton kernel: [ 7633.316012] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Apr 7 21:37:50 benton kernel: [ 7633.316012] Process mount.zfs (pid: 2710, threadinfo ffff88000c834000, task ffff88004bf11720)
Apr 7 21:37:50 benton kernel: [ 7633.316012] Stack:
Apr 7 21:37:50 benton kernel: [ 7633.316012] ffff88000c835d58 ffffffffa01d4a96 ffff880077f56500 ffff880043a02c00
Apr 7 21:37:50 benton kernel: [ 7633.316012] ffff88000c835d78 ffffffff8116abac fffffffffffffff0 00000000fffffff0
Apr 7 21:37:50 benton kernel: [ 7633.316012] ffff88000c835da8 ffffffff8116b0b3 ffff880066ce1e00 ffffffffa01fe4c0
Apr 7 21:37:50 benton kernel: [ 7633.316012] Call Trace:
Apr 7 21:37:50 benton kernel: [ 7633.316012] [] zpl_kill_sb+0x16/0x30 [zfs]
Apr 7 21:37:50 benton kernel: [ 7633.316012] [] deactivate_locked_super+0x3c/0x90
Apr 7 21:37:50 benton kernel: [ 7633.316012] [] mount_nodev+0xb3/0xc0
Apr 7 21:37:50 benton kernel: [ 7633.316012] [] zpl_mount+0x25/0x30 [zfs]
Apr 7 21:37:50 benton kernel: [ 7633.316012] [] mount_fs+0x43/0x1b0
Apr 7 21:37:50 benton kernel: [ 7633.316012] [] vfs_kern_mount+0x6a/0xc0
Apr 7 21:37:50 benton kernel: [ 7633.316012] [] do_kern_mount+0x54/0x110
Apr 7 21:37:50 benton kernel: [ 7633.316012] [] do_mount+0x1a4/0x260
Apr 7 21:37:50 benton kernel: [ 7633.316012] [] sys_mount+0x90/0xe0
Apr 7 21:37:50 benton kernel: [ 7633.316012] [] system_call_fastpath+0x16/0x1b
Apr 7 21:37:50 benton kernel: [ 7633.316012] Code: 05 00 00 48 c7 c6 5b 0f 1e a0 48 c7 c7 10 1b 1f a0 e8 b5 40 ed ff e9 c0 fe ff ff 55 48 89 e5 66 66 66 66 90 48 8b bf 88 02 00 00
Apr 7 21:37:50 benton kernel: [ 7633.316012] RIP [] zfs_preumount+0x10/0x30 [zfs]
Apr 7 21:37:50 benton kernel: [ 7633.316012] RSP
Apr 7 21:37:50 benton kernel: [ 7633.316012] CR2: 0000000000000400
Apr 7 21:37:50 benton kernel: [ 7633.445763] ---[ end trace 3e9bcc415a5c01e8 ]---

[behlendorf]

Gunnar actually caught and fixed this issue in the latest source, see issue #639 and commit 1f0d8a5