linux-ext4 - Re: [PATCH v3 15/17] ext4: convert free groups order lists to xarrays

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Message-ID: <20250724045456.GA80823@mit.edu>
Date: Thu, 24 Jul 2025 00:54:56 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Baokun Li <libaokun1@...wei.com>, linux-ext4@...r.kernel.org,
        adilger.kernel@...ger.ca, jack@...e.cz, linux-kernel@...r.kernel.org,
        ojaswin@...ux.ibm.com, julia.lawall@...ia.fr, yi.zhang@...wei.com,
        yangerkun@...wei.com, libaokun@...weicloud.com
Subject: Re: [PATCH v3 15/17] ext4: convert free groups order lists to xarrays

On Wed, Jul 23, 2025 at 08:55:14PM -0700, Guenter Roeck wrote:
> Hi,
> 
> On Mon, Jul 14, 2025 at 09:03:25PM +0800, Baokun Li wrote:
> > While traversing the list, holding a spin_lock prevents load_buddy, making
> > direct use of ext4_try_lock_group impossible. This can lead to a bouncing
> > scenario where spin_is_locked(grp_A) succeeds, but ext4_try_lock_group()
> > fails, forcing the list traversal to repeatedly restart from grp_A.
> > 
> 
> This patch causes crashes for pretty much every architecture when
> running unit tests as part of booting.

I'm assuming that you're using a randconfig that happened to enable
CONFIG_EXT4_KUNIT_TESTS=y.

A simpler reprducer is to have a .kunitconfig containing:

CONFIG_KUNIT=y
CONFIG_KUNIT_TEST=y
CONFIG_KUNIT_EXAMPLE_TEST=y
CONFIG_EXT4_KUNIT_TESTS=y

... and then run :./tools/testing/kunit/kunit.py run".

The first failure is actually with [11/17] ext4: fix largest free
orders lists corruption on mb_optimize_scan switch, which triggers a
failure of test_mb_mark_used.

Baokun, can you take a look please?   Many thanks!

	    	       	    	      - Ted