Re: Blocked tasks on 3.15.1

[Chris Mason <clm@fb.com>]

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