Re: Blocked tasks on 3.15.1

[Cody P Schafer <dev@codyps.com>]

On Mon, Jun 30, 2014 at 1:30 PM, Chris Mason <clm@fb.com> wrote:
> On 06/30/2014 02:11 PM, Chris Mason wrote:
>> On 06/29/2014 04:02 PM, Cody P Schafer wrote:
>>> On Fri, Jun 27, 2014 at 7:22 PM, Chris Samuel <chris@csamuel.org> wrote:
>>>> On Fri, 27 Jun 2014 05:20:41 PM Duncan wrote:
>>>>
>>>>> If I'm not mistaken the fix for the 3.16 series bug was:
>>>>>
>>>>> ea4ebde02e08558b020c4b61bb9a4c0fcf63028e
>>>>>
>>>>> Btrfs: fix deadlocks with trylock on tree nodes.
>>>>
>>>> That patch applies cleanly to 3.15.2 so if it is indeed the fix it should
>>>> probably go to -stable for the next 3.15 release..
>>>>
>>>> Unfortunately my test system died a while ago (hardware problem) and I've not
>>>> been able to resurrect it yet.
>>>
>>> I'm also seeing stuck tasks on btrfs (3.14.4, 3.15.1, 3.15.2).
>>> I've also tried 3.15.2 with ea4ebde02e08558b020c4b61bb9a4c applied on
>>> top with similar results.
>>> I've been triggering the hang with 'rsync -hPaHAXx --del /mnt/home/a/
>>> /home/a/' where /mnt/home and /home are 2 separate btrfs filesystems
>>> on 2 separate disks.
>>>
>>> dmesg with w-trigger: http://bpaste.net/show/419555
>>> --
>>
>> These traces show us waiting for IO, but it doesn't show anyone doing
>> the IO.  Either we're failing to kick off our work queues or they are
>> stuck on something else.
>>
>> Could you please send a sysrq-t and sysrq-l while you're stuck?  That
>> will show us all the procs and all the CPUs.
>
> Also, do you have any nodatacow files in here?  Please say yes.
>

kernel log from 3.15.2 + ea4ebde02 showing the blocked tasks,
sysrq-{w,t,l} included
http://bpaste.net/show/423296/

I haven't explicitely created any nodatacow files, is there a quick
way to tell if there are any? Right now I'm doing
`lsattr -R /mnt/home/a/ 2>/dev/null | grep -- '^-*C-* '` to try and check.

(2>/dev/null is hiding lots of "Operation not supported While reading
flags on" warnings)