Re: Blocked tasks on 3.15.1

[Torbjørn <lists@skagestad.org>]

On 07/22/2014 09:50 PM, Chris Mason wrote:
> On 07/22/2014 03:42 PM, Torbjørn wrote:
>> On 07/22/2014 04:53 PM, Chris Mason wrote:
>>> On 07/19/2014 02:23 PM, Martin Steigerwald wrote:
>>>
>>>>> Running 3.15.6 with this patch applied on top:
>>>>>    - still causes a hang with `rsync -hPaHAXx --del /mnt/home/nyx/
>>>>> /home/nyx/`
>>>>> - no extra error messages printed (`dmesg | grep racing`) compared to
>>>>> without the patch
>>>> I got same results with 3.16-rc5 + this patch (see thread BTRFS hang
>>>> with
>>>> 3.16-rc5). 3.16-rc4 still is fine with me. No hang whatsoever so far.
>>>>
>>>>> To recap some details (so I can have it all in one place):
>>>>>    - /home/ is btrfs with compress=lzo
>>>> BTRFS RAID 1 with lzo.
>>>>
>>>>>    - I have _not_ created any nodatacow files.
>>>> Me neither.
>>>>
>>>>>    - Full stack is: sata <-> dmcrypt <-> lvm <-> btrfs (I noticed others
>>>>> mentioning the use of dmcrypt)
>>>> Same, except no dmcrypt.
>>>>
>>> Thanks for the help in tracking this down everyone.  We'll get there!
>>> Are you all running multi-disk systems (from a btrfs POV, more than one
>>> device?)  I don't care how many physical drives this maps to, just does
>>> btrfs think there's more than one drive.
>>>
>>> -chris
>> 3.16-rc6 with your patch on top still causes hangs here.
>> No traces of "racing" in dmesg
>> Hang is on a btrfs raid 0 consisting of 3 drives.
>> Full stack is: sata <-> dmcrypt <-> btrfs raid0
>>
>> Hang was caused by
>> 1. Several rsync -av --inplace --delete <source> <backup subvol>
>> 2. btrfs subvolume snapshot -r <backup subvol> <bacup snap>
>>
>> The rsync jobs are done one at a time
>> btrfs is stuck when trying to create the read only snapshot
> The trace is similar, but you're stuck trying to read the free space
> cache.  This one I saw earlier this morning, but I haven't seen these
> parts from the 3.15 bug reports.
>
> Maybe they are related though, I'll dig into the 3.15 bug reports again.
>
> -chris
In case it was not clear, this hang was on a different btrfs volume than 
the 3.15 hang (but the same server).
Earlier the affected volume was readable during the hang. This time the 
volume is not readable either.

I'll keep the patched 3.16 running and see if I can trigger something 
similar to the 3.15 hang.

Thanks

--
Torbjørn