Bug 216559 - btrfs crash root mount RAID0 caused by ac0677348f3c2

Bug 216559 - btrfs crash root mount RAID0 caused by ac0677348f3c2

[Thorsten Leemhuis]

Hi, this is your Linux kernel regression tracker speaking.

David, I noticed a regression report in bugzilla.kernel.org apparently
caused by a changed of yours. As many (most?) kernel developer don't
keep an eye on the bug-tracker, I decided to forward the report by mail.
Quoting from https://bugzilla.kernel.org/show_bug.cgi?id=216559 :

> [reply] [−] Description Viktor Kuzmin 2022-10-08 20:41:32 UTC
> 
> In linux 6.0.0 there was change in block-group.c file in function btrfs_rmap_block:
> [...]

FWIW, the reporter (CCed) here meant change ac0677348f3c2 ("btrfs: merge
calculations for simple striped profiles in btrfs_rmap_block").
Reverting it fixes the problem.

> After this change I have a crash with DIVIDE by ZERO error. It seems that map->sub_stripes can be zero.
> 
> My setup is 2x 1TB nvme with space_cache=v2 and discard=async btrfs raid0.

See the ticket for more details and screenshots from the crash.

BTW, let me use this mail to also add the report to the list of tracked
regressions to ensure it's doesn't fall through the cracks:

#regzbot introduced: ac0677348f3c2
https://bugzilla.kernel.org/show_bug.cgi?id=216559
#regzbot ignore-activity

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)

P.S.: As the Linux kernel's regression tracker I deal with a lot of
reports and sometimes miss something important when writing mails like
this. If that's the case here, don't hesitate to tell me in a public
reply, it's in everyone's interest to set the public record straight.

Re: Bug 216559 - btrfs crash root mount RAID0 caused by ac0677348f3c2

[David Sterba]

On Tue, Oct 11, 2022 at 02:09:50PM +0200, Thorsten Leemhuis wrote:
> Hi, this is your Linux kernel regression tracker speaking.
> 
> David, I noticed a regression report in bugzilla.kernel.org apparently
> caused by a changed of yours. As many (most?) kernel developer don't
> keep an eye on the bug-tracker, I decided to forward the report by mail.
> Quoting from https://bugzilla.kernel.org/show_bug.cgi?id=216559 :

Thanks, you don't need to forward the mails as I'm on CC of all bugzilla
updates where the btrfs virtual assignee is also present. But feel free
to ping regarding any regressions you're tracking and would like an
update.

Inspired by the LPC talk about bugzilla I went through all 650+ btrfs
bugs and closed what looked either fixed or not relevant anymore. The
rest are recent reports or bugs that may need to be moved elsewhere.
As kernel.org bugzilla is recommended for reports in our community
documentation I monitor new bugs but with variable reaction time.

Re: Bug 216559 - btrfs crash root mount RAID0 caused by ac0677348f3c2

[Thorsten Leemhuis]

On 14.10.22 13:07, David Sterba wrote:
> On Tue, Oct 11, 2022 at 02:09:50PM +0200, Thorsten Leemhuis wrote:
>> Hi, this is your Linux kernel regression tracker speaking.
>>
>> David, I noticed a regression report in bugzilla.kernel.org apparently
>> caused by a changed of yours. As many (most?) kernel developer don't
>> keep an eye on the bug-tracker, I decided to forward the report by mail.
>> Quoting from https://bugzilla.kernel.org/show_bug.cgi?id=216559 :
> 
> Thanks, you don't need to forward the mails as I'm on CC of all bugzilla
> updates where the btrfs virtual assignee is also present.

Hmmm. Do you want to make my life easier or want to get less mail? I
thought about this for a while. Unless you strongly object, I would like
to continue forwarding them for the following reasons:

* you might be on vacation or AFK for other reasons; your Comaintainers
that were CCed would know and likely then help out
* CCing the list makes other people notice the issue and gives them a
chance to help (Qu Wenruo replied in bugzilla shortly after I sent the
mail you quoted, which might or might not be due to my mail).
* regression tracking is hard already; it would make it a lot harder if
I'm forced to make and maintain notes how each and every maintainer
would like me to handle situations like this
* right now I need to send one mail anyway to add a regression to the
tracking

> But feel free
> to ping regarding any regressions you're tracking and would like an
> update.

Great, thx!

> Inspired by the LPC talk about bugzilla I went through all 650+ btrfs
> bugs and closed what looked either fixed or not relevant anymore. The
> rest are recent reports or bugs that may need to be moved elsewhere.
> As kernel.org bugzilla is recommended for reports in our community
> documentation I monitor new bugs but with variable reaction time.

Thx for your work and good to know that you are referring to it.

Ciao, Thorsten

Re: Bug 216559 - btrfs crash root mount RAID0 caused by ac0677348f3c2

[David Sterba]

On Mon, Oct 17, 2022 at 02:00:30PM +0200, Thorsten Leemhuis wrote:
> On 14.10.22 13:07, David Sterba wrote:
> > On Tue, Oct 11, 2022 at 02:09:50PM +0200, Thorsten Leemhuis wrote:
> >> Hi, this is your Linux kernel regression tracker speaking.
> >>
> >> David, I noticed a regression report in bugzilla.kernel.org apparently
> >> caused by a changed of yours. As many (most?) kernel developer don't
> >> keep an eye on the bug-tracker, I decided to forward the report by mail.
> >> Quoting from https://bugzilla.kernel.org/show_bug.cgi?id=216559 :
> > 
> > Thanks, you don't need to forward the mails as I'm on CC of all bugzilla
> > updates where the btrfs virtual assignee is also present.
> 
> Hmmm. Do you want to make my life easier or want to get less mail? I
> thought about this for a while. Unless you strongly object, I would like
> to continue forwarding them for the following reasons:
> 
> * you might be on vacation or AFK for other reasons; your Comaintainers
> that were CCed would know and likely then help out
> * CCing the list makes other people notice the issue and gives them a
> chance to help (Qu Wenruo replied in bugzilla shortly after I sent the
> mail you quoted, which might or might not be due to my mail).
> * regression tracking is hard already; it would make it a lot harder if
> I'm forced to make and maintain notes how each and every maintainer
> would like me to handle situations like this
> * right now I need to send one mail anyway to add a regression to the
> tracking

No problem with continuing the way it is, the reasons above make sense.

Re: Bug 216559 - btrfs crash root mount RAID0 caused by ac0677348f3c2 #forregzbot

[Thorsten Leemhuis]

[Note: this mail is primarily send for documentation purposes and/or for
regzbot, my Linux kernel regression tracking bot. That's why I removed
most or all folks from the list of recipients, but left any that looked
like a mailing lists. These mails usually contain '#forregzbot' in the
subject, to make them easy to spot and filter out.]

On 11.10.22 14:09, Thorsten Leemhuis wrote:

> 
> David, I noticed a regression report in bugzilla.kernel.org apparently
> caused by a changed of yours. As many (most?) kernel developer don't
> keep an eye on the bug-tracker, I decided to forward the report by mail.
> Quoting from https://bugzilla.kernel.org/show_bug.cgi?id=216559 :

Regzbot for some reason missed the fix. :-/

#regzbot fixed-by: 76a66ba10132