zpool import read-only

[behlendorf]

Observed when importing a pool read-only, v0.6.2-97_g09d672d.

VERIFY(zio->io_type != ZIO_TYPE_WRITE || spa_writeable(spa)) failed
SPLError: 9415:0:(zio.c:2613:zio_vdev_io_start()) SPL PANIC
SPL: Showing stack for process 9415
Pid: 9415, comm: z_null_iss/0 Tainted: P           ----------------   2.6.32-220.1chaos.2012010958.16kstack.ch5.x86_64 #1
Call Trace:
 [<ffffffffa03f25a7>] ? spl_debug_dumpstack+0x27/0x40 [spl]
 [<ffffffffa03f3d51>] ? spl_debug_bug+0x81/0xd0 [spl]
 [<ffffffffa059bc81>] ? zio_vdev_io_start+0x2d1/0x2e0 [zfs]
 [<ffffffffa059b5f3>] ? zio_execute+0xb3/0x140 [zfs]
 [<ffffffffa03fc858>] ? taskq_thread+0x218/0x4b0 [spl]
 [<ffffffff814ee400>] ? thread_return+0x4e/0x77e
 [<ffffffff8105fa50>] ? default_wake_function+0x0/0x20
 [<ffffffffa03fc640>] ? taskq_thread+0x0/0x4b0 [spl]
 [<ffffffff81090886>] ? kthread+0x96/0xa0
 [<ffffffff8100c14a>] ? child_rip+0xa/0x20
 [<ffffffff810907f0>] ? kthread+0x0/0xa0
 [<ffffffff8100c140>] ? child_rip+0x0/0x20

[behlendorf]

This is reproducible in 0.6.2 so it's not a regression. It appears to occur because it's attempting to initialize a cache device and obviously that's not possible when the pool is readonly. I'm surprised this wasn't noticed before.

[behlendorf]

0904c2b appears to work correctly although I'm not 100% sure we can skip all of this validation. This should be perhaps be more targeted. I also don't see why this issue wouldn't impact Illumos/FreeBSD so we should attempt to reproduce it there. @csiden I've checked the Illumos tracker and I don't see anything like this, have you heard of any similar reports?

[b333z]

I was able to replicate that import panic when readonly with cache vdev on FreeBSD 9.2 RELEASE amd64:

# zfs create tank/test
# zfs create -V 100M tank/test/m1
# zfs create -V 100M tank/test/m2
# zfs create -V 100M tank/test/c1
# zpool create test mirror /dev/zvol/tank/test/m1 /dev/zvol/tank/test/m2
# zpool export test
# zpool import -d /dev/zvol/tank/test/ test
# zpool export test
# zpool import -o readonly=on -d /dev/zvol/tank/test/ test
# zpool export test
# zpool import -d /dev/zvol/tank/test/ test
# zpool add test cache /dev/zvol/tank/test/c1
# zpool export test
# zpool import -o readonly=on -d /dev/zvol/tank/test/ test

Results in this panic:

Have my first nightly running on an OpenIndiana that I setup a while back, so if that works I'll try the same there.

[csiden]

@behlendorf I tried out the steps @b333z mentioned and was able to reproduce the issue on illumos, so it looks like it's a problem for everyone.

[behlendorf]

@csiden Thanks for checking, any thoughts on the fix 0904c2b.

[csiden]

@behlendorf I asked George to take a look at it and he said he's almost ready with a better fix (he's running regression tests now). I'll post an update when his fix is ready (he says it should be small and simple).

[csiden]

George's fix for this is in illumos now: illumos/illumos-gate@973c78e

I tested out @b333z's steps with this fix and was no longer able to reproduce the bug.

[behlendorf]

@csiden Thanks for the link, I like George's fix much better we'll merge it shortly too.