[OmniOS-discuss] "zpool import" triggers deadlock in somes cases ? (metaslab_group_taskqs)

[Youzhong Yang]

This could be the following issue:

https://www.illumos.org/issues/4730



On Mon, Apr 28, 2014 at 9:17 AM, Alex <alex.ranskis at gmail.com> wrote:

> Hello,
>
> I'm trying to understand this behavior, which I see on servers connected
> to an external disk enclosure. (I cannot reproduce it on a simple 1 disk VM)
>
> # kstat -c taskq | grep metaslab_group_tasksq| wc -l
> 1112
>
> # zpool import >/dev/null
>
> # kstat -c taskq | grep metaslab_group_tasksq| wc -l
> 1160
>
>
> we are accumulating 'metaslab_group_taskqs'
>
> module: unix                            instance: 513
> name:   metaslab_group_tasksq           class:    taskq
>         crtime                          842173.739164514
>         executed                        0
>         maxtasks                        0
>         nactive                         0
>         nalloc                          0
>         pid                             0
>         priority                        60
>         snaptime                        842774.7092530ok 06
>         tasks                           0
>         threads                         3
>         totaltime                       0
>
>
> The "zpool import" command itself runs fine. I get the same behavior
> whether there are pools to import or not.
>
> but kernel threads are piling up, for each CV there are 3 threads :
> > ffffff05844fe080::wchaninfo -v
> ADDR             TYPE NWAITERS   THREAD           PROC
> ffffff05844fe080 cond        3:  ffffff0021c58c40 sched
>                                  ffffff0021c5ec40 sched
>                                  ffffff0021c64c40 sched
>
> and they're all blocking, with a similar stack :
> > ffffff0021c58c40::findstack -v
> stack pointer for thread ffffff0021c58c40: ffffff0021c58a80
> [ ffffff0021c58a80 _resume_from_idle+0xf4() ]
>   ffffff0021c58ab0 swtch+0x141()
>   ffffff0021c58af0 cv_wait+0x70(ffffff05844fe080, ffffff05844fe070)
>   ffffff0021c58b60 taskq_thread_wait+0xbe(ffffff05844fe050,
> ffffff05844fe070, ffffff05844fe080, ffffff0021c58bc0, ffffffffffffffff)
>   ffffff0021c58c20 taskq_thread+0x37c(ffffff05844fe050)
>   ffffff0021c58c30 thread_start+8()
>
>
> the taskq seems to be created by a call to metaslab_group_create(), here :
>               zfs`vdev_alloc+0x54a
>               zfs`spa_config_parse+0x48
>               zfs`spa_config_parse+0xda
>               zfs`spa_config_valid+0x78
>               zfs`spa_load_impl+0xa81
>               zfs`spa_load+0x14e
>               zfs`spa_tryimport+0xaa
>               zfs`zfs_ioc_pool_tryimport+0x51
>               zfs`zfsdev_ioctl+0x4a7
>               genunix`cdev_ioctl+0x39
>               specfs`spec_ioctl+0x60
>               genunix`fop_ioctl+0x55
>               genunix`ioctl+0x9b
>               unix`sys_syscall32+0xff
>
>
> I'm out of my depth here, any pointer to investigate further would be much
> appreciated !
>
> cheers,
> alex
>
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