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

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Date:   Mon, 17 Jul 2023 17:34:24 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ritesh Harjani <ritesh.list@...il.com>
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!

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.

Cheers,

					- Ted