Re: ZFS operations hanging, but no visible errors?

From: Chris Ross <cross+freebsd_at_distal.com>
Date: Fri, 05 Nov 2021 16:59:47 UTC 

> On Nov 5, 2021, at 12:39, Fabian Keil <freebsd-listen@fabiankeil.de> wrote:
> You can check with "procstat -kk" where the hanging
> processes are stuck.

Running prostate -kk on the rsync that was hung, then killed, then SIGKILL’d shows:

procstat -kk 35220
  PID    TID COMM                TDNAME              KSTACK
35220 102499 rsync               -                   mi_switch+0xc1 _sleep+0x1cb vm_wait_doms+0xe2 vm_wait_domain+0x51 vm_domain_alloc_fail+0x86 vm_page_alloc_domain_after+0x7e uma_small_alloc+0x58 keg_alloc_slab+0xba zone_import+0xee zone_alloc_item+0x6f abd_alloc_chunks+0x61 abd_alloc+0x102 arc_hdr_alloc_abd+0xb0 arc_hdr_alloc+0x11e arc_read+0x4f4 dbuf_issue_final_prefetch+0x108 dbuf_prefetch_impl+0x3d0 dmu_zfetch+0x558


> 
> The output of:
> dtrace -qn 'zfs-dbgmsg {printf("%Y: %s\n", walltimestamp, stringof(arg0))}'
> could be useful as well.

I’ve run 

% sudo dtrace -qn 'zfs-dbgmsg {printf("%Y: %s\n", walltimestamp, stringof(arg0))}’

But, it’s yielding no output.  Is that normal because it outputs information about operations (which aren’t happening), or should it’s output have been immediate?

- Chris