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

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Message-ID: <20230718091031.GB1140910@pevik>
Date:   Tue, 18 Jul 2023 11:10:31 +0200
From:   Petr Vorel <pvorel@...e.cz>
To:     Ritesh Harjani <ritesh.list@...il.com>
Cc:     Theodore Ts'o <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
        open list <linux-kernel@...r.kernel.org>,
        lkft-triage@...ts.linaro.org, linux-mm <linux-mm@...ck.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Dan Carpenter <dan.carpenter@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        LTP List <ltp@...ts.linux.it>,
        Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Subject: Re: [LTP] 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,

Hi Ted, Ritesh, all,

> 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

Late, but better than never: LTP C tests can be run without any wrapper.
e.g. to reproduce the bug triggered by fs_fill, you can just:

git clone https://github.com/linux-test-project/ltp.git && cd ltp
./ci/your-distro.sh # optionally install the dependencies
make autotools
./configure
cd testcases/kernel/fs/fs_fill/
make -j`nproc`
while true; do ./fs_fill; sleep 1; done

NOTE: runltp is
1) deprecated, replaced by runltp-ng [1]
2) again, there is no need to use this shell wrapper to run a single C binary

Kind regards,
Petr

[1] https://github.com/linux-test-project/runltp-ng

> 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