Re: [Xen-users] PROBLEM: Kernel BUG with raid5 soft + Xen + DRBD - invalid opcode

[MasterPrenium <masterprenium.lkml@xxxxxxxxx>]

Hi guys,

My issue is still remaining with new kernels, at least last revision of 
4.10.x branch.
But I found something that can be interesting for investigations, here I 
attached another .config file for kernel building, with this 
configuration I'm not able to reproduce the kernel panic, I got no crash 
at all with exactly the same procedure.
Tested on 4.9.16 kernel and 4.10.13 :
- config_Crash.txt : result in a crash running fio within less than 2 
minutes
- config_NoCrash.txt : even after hours of fio, rebuilding arrays, etc 
... no crash at all, neither no warning or anything in dmesg.
Note : config_NoCrash is coming from another server on which I had setup 
similar system and which was not crashing. Tested this kernel on my 
crashing system, and no crash anymore...
I can't believe how a different config can solve a kernel BUG...

If someone has any idea...

Bests,


Le 09/01/2017 à 23:44, Shaohua Li a écrit :
> On Sun, Jan 08, 2017 at 02:31:15PM +0100, MasterPrenium wrote:
> > Hello,
> >
> > Replies below + :
> > - I don't know if this can help but after the crash, when the system
> > reboots, the Raid 5 stack is re-synchronizing
> > [   37.028239] md10: Warning: Device sdc1 is misaligned
> > [   37.028541] created bitmap (15 pages) for device md10
> > [   37.030433] md10: bitmap initialized from disk: read 1 pages, set 59 of
> > 29807 bits
> >
> > - Sometimes the kernel completely crash (lost serial + network connection),
> > sometimes only got the "BUG" dump, but still have network access (but a
> > reboot is impossible, need to reset the system).
> >
> > - You can find blktrace here (while running fio), I hope it's complete since
> > the end of the file is when the kernel crashed : https://goo.gl/X9jZ50
> Looks most are normal full stripe writes.
>   
> > > I'm trying to reproduce, but no success. So
> > > ext4->btrfs->raid5, crash
> > > btrfs->raid5, no crash
> > > right? does subvolume matter? When you create the raid5 array, does adding
> > > '--assume-clean' option change the behavior? I'd like to narrow down the issue.
> > > If you can capture the blktrace to the raid5 array, it would be great to hint
> > > us what kind of IO it is.
> > Yes Correct.
> > The subvolume doesn't matter.
> > -- assume-clean doesn't change the behaviour.
> so it's not a resync issue.
>
> > Don't forget that the system needs to be running on xen to crash, without
> > (on native kernel) it doesn't crash (or at least, I was not able to make it
> > crash).
> > > > Regarding your patch, I can't find it. Is it the one sent by Konstantin
> > > > Khlebnikov ?
> > > Right.
> > It doesn't help :(. Maybe the crash is happening a little bit later.
> ok, the patch is unlikely helpful, since the IO size isn't very big.
>
> Don't have good idea yet. My best guess so far is virtual machine introduces
> extra delay, which might trigger some race conditions which aren't seen in
> native.  I'll check if I could find something locally.
>
> Thanks,
> Shaohua

Attachment: Config_Crash.txt
Description: Text document

Attachment: Config_NoCrash.txt
Description: Text document

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