Created attachment 193578 [details]
zpool status hangs on [spa_namespace_lock]. Output of the procstat -a -kk and pictures of the stack trace from thread holding the lock attached.
From Andriy Gapon <avg@FreeBSD.org>:
13 100015 geom g_event mi_switch+0xe6
sleepq_wait+0x2c _sx_xlock_hard+0x314 zvol_geom_access+0x148 g_access+0x1fd
g_eli_read_metadata+0x249 g_eli_config+0x3ed g_run_events+0x13e fork_exit+0x83
930 100354 zfsd - mi_switch+0xe6
sleepq_wait+0x2c _sleep+0x23e g_access+0xf7 vdev_geom_attach+0x61c
vdev_attach_ok+0x29 vdev_geom_open+0x394 vdev_open+0x115
vdev_open_children+0x30 vdev_root_open+0x3a vdev_open+0x115
spa_ld_mos_with_trusted_config+0x19 spa_load+0x5c spa_load_best+0x6b
I think I know what's going on in your case (not sure if it's the same a as
previous reports in this bug). It's probably a consequence of base r330977, a
fix to bug 225960.
I didn't fully realize at that time, but that commit introduced a "g_access
lock" in disguise.
So, we went from a LOR between geom topology lock and spa_namespace_lock to a
race caused by dropping the topology lock to a LOR between spa_namespace_lock
and "g_access lock".
The toughest part now is to decide how to solve the LOR without re-introducing
the race. Or alternatively, how to solve the race without introducing a
Created attachment 193579 [details]
Created attachment 193580 [details]
Stack trace part 1
Created attachment 193581 [details]
Stack trace part 2
I can test patches, produce and provide link to the coredump and whatever else is necessary -- machine is under my total control and could be taken offline at will. The only caveat is that the CPU there is not all that powerful -- complete rebuild of the kernel will take several hours.