Re: btrfs scrub crashes OS

[Lukas Pirl <btrfs@lukas-pirl.de>]

Dear Qu,

thanks for your reply.

On 09/25/2017 12:19 PM, Qu Wenruo wrote as excerpted:
> Even no dmesg output using tty or netconsole?

And thanks for the pointer to netconsole, I tried that one.
No success. I set netconsole up, verified it worked, started a scrub,
the machine went away after a couple of hours, netconsole empty.

> That's strange.
> Normally it should be kernel BUG_ON() to cause such problem.
>  
> And if the system is still responsible (either from TTY or ssh), is
> there anything strange like tons of IO or CPU usage?

I can't tell, the machine just disappears from the network. Dead. IIRC,
it was also all dead when I sat in front of it.

> Btrfs-progs v4.13 should have fixed it.
> As long as v4.13 btrfs check reports no error, its metadata should be
> good.

I can try that one, if helpful.

> You could try the out-of-tree offline scrub to do a full scrub of your
> fs unmounted, so it won't crash your system (if nothing wrong happened)
> https://github.com/gujx2017/btrfs-progs/tree/offline_scrub

Did that, machine crashed again.

>>    MIXED_BACKREF, BIG_METADATA, EXTENDED_IREF, SKINNY_METADATA, NO_HOLES
> 
> Only NO_HOLES is not ordinary, but shouldn't cause a problem.

Would it be sensible to turn that feature off using `btrfstune` (if
possible at all)?

> Without kernel backtrace, it's tricky to locate the problem.
> So I would recommend to use netconsole (IIRC more reliable, as I use it
> on my test VM to capture the dying message) or TTY output to verify
> there is no kernel message/backtrace.

Yeah I see we are in a tricky situation here.

I will try to scrub with autodefrag and compression deactivated.

Could a full balance be of any help? At least to find out if it crashes
the machine as well?

Cheers,

Lukas

> Thanks,
> Qu
> 
>>    no quotas in use
>>    see also https://pastebin.com/4me6zDsN for more details
>> btrfs-progs v4.12
>> GNU/Linux 4.12.0-0.bpo.1-amd64 #1 SMP Debian 4.12.6-1~bpo9+1 x86_64
>>
>> The question, obviously, is how can I make this fs "scrubable" again?
>> Are the errors found by btrfsck safe to repair using btrfsck or some
>> other tool?
>>
>> Thank you so much in advance,
>>
>> Lukas
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