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

[Guenter Roeck <linux@roeck-us.net>]

On Thu, Jul 24, 2025 at 07:14:58PM +0800, Zhang Yi wrote:
> On 2025/7/24 12:54, Theodore Ts'o wrote:
> > 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!
> > 
> 
> Hi Ted and Guenter,
> 
> I'm sorry for this regression, we didn't run these tests. Baokun is
> currently on a business trip, so I help to look into this issue. The
> reason for the failure is that the variable initialization in the
> mb unit tests are insufficient, but this series relies on them.
> 
> Could you please try the following diff? I have tested it on my
> machine, and the issue does not recur. If every thing looks fine, I
> will send out the official patch.
> 

Confirmed to fix the problem. Please feel free to add

Tested-by: Guenter Roeck <linux@roeck-us.net>

Thanks,
Guenter

> Thanks,
> Yi.
> 
> 
> diff --git a/fs/ext4/mballoc-test.c b/fs/ext4/mballoc-test.c
> index d634c12f1984..a9416b20ff64 100644
> --- a/fs/ext4/mballoc-test.c
> +++ b/fs/ext4/mballoc-test.c
> @@ -155,6 +155,7 @@ static struct super_block *mbt_ext4_alloc_super_block(void)
>  	bgl_lock_init(sbi->s_blockgroup_lock);
> 
>  	sbi->s_es = &fsb->es;
> +	sbi->s_sb = sb;
>  	sb->s_fs_info = sbi;
> 
>  	up_write(&sb->s_umount);
> @@ -802,6 +803,8 @@ static void test_mb_mark_used(struct kunit *test)
>  	KUNIT_ASSERT_EQ(test, ret, 0);
> 
>  	grp->bb_free = EXT4_CLUSTERS_PER_GROUP(sb);
> +	grp->bb_largest_free_order = -1;
> +	grp->bb_avg_fragment_size_order = -1;
>  	mbt_generate_test_ranges(sb, ranges, TEST_RANGE_COUNT);
>  	for (i = 0; i < TEST_RANGE_COUNT; i++)
>  		test_mb_mark_used_range(test, &e4b, ranges[i].start,
> @@ -875,6 +878,8 @@ static void test_mb_free_blocks(struct kunit *test)
>  	ext4_unlock_group(sb, TEST_GOAL_GROUP);
> 
>  	grp->bb_free = 0;
> +	grp->bb_largest_free_order = -1;
> +	grp->bb_avg_fragment_size_order = -1;
>  	memset(bitmap, 0xff, sb->s_blocksize);
> 
>  	mbt_generate_test_ranges(sb, ranges, TEST_RANGE_COUNT);
> 
> 
>