linux-kernel - Re: next: kernel BUG at fs/ext4/mballoc.c:4369!

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Date:   Tue, 18 Jul 2023 07:27:16 +0530
From:   Ritesh Harjani (IBM) <ritesh.list@...il.com>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, lkft-triage@...ts.linaro.org,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        LTP List <ltp@...ts.linux.it>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Dan Carpenter <dan.carpenter@...aro.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Subject: Re: next: kernel BUG at fs/ext4/mballoc.c:4369!

"Theodore Ts'o" <tytso@....edu> writes:

> On Mon, Jul 17, 2023 at 08:04:54PM +0530, Ritesh Harjani wrote:
>> 
>> These can basically trigger in extremely low memory space and only when
>> such ranges exist in the PA rbtree. Hence, I guess it is a little hard
>> to tigger race.
>
> Ritesh, thanks for looking into this!
>
> Naresh, how easy is it for you to trigger the BUG when using LTP?  I
> did two xfstests runs using "gce-xfstests -c ext2/default -g auto",
> one on the ext4 dev branch, and one on linux-next 20230717, and I
> wasn't able to trigger the BUG.
>
> If you can trivially trigger it using LTP (perhaps with a low memory
> configuration in your test setup?), that would be useful to know.

Hi Ted,

Sorry for wrong choice of words. By low memory space I meant low disk
space i.e. ENOSPC test (fs_fill). I reproduced it like this - 

root@...ntu:/opt/ltp# while [ 1 ]; do ./runltp -s fs_fill; sleep 1; done

For me it took around ~1-2 hours for it to reproduce when I tried again.
I am hoping if we run generic/269 (fsstress ENOSPC) in a while loop like
this maybe it can hit this bug. But I didn't give it a shot.

-ritesh