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

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Message-ID: <20250724145437.GD80823@mit.edu>
Date: Thu, 24 Jul 2025 10:54:37 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: Zhang Yi <yi.zhang@...wei.com>
Cc: Guenter Roeck <linux@...ck-us.net>, 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, yangerkun@...wei.com, libaokun@...weicloud.com
Subject: Re: [PATCH v3 15/17] ext4: convert free groups order lists to xarrays

On Thu, Jul 24, 2025 at 07:14:58PM +0800, Zhang Yi wrote:
> 
> I'm sorry for this regression, we didn't run these tests.

No worries, I didn't run them either.

> 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.

This patch fixes the test bug which was causing the failure of
test_new_blocks_simple.

However, there is still test failure of test_mb_mark_used in the patch
series starting with bbe11dd13a3f ("ext4: fix largest free orders
lists corruption on mb_optimize_scan switch").  The test failure is
fixed by 458bfb991155 ("ext4: convert free groups order lists to
xarrays").  The reason why this is especialy problematic is that
commit which introduced the problem is marked as "cc: stable", which
means it will get back ported to LTS kernels, thus introducing a
potential bug.

One of the advantages of unit tests is that they are light weight
enough that it is tractable to run them against every commit in the
patch series.  So we should strive to add more unit tests, since it
makes easier to detect regressions.

Anyway, here's the stack trace staring with "ext4: fix largest free
orders lists corruption on mb_optimize_scan switch".  Could you
investigate this failure?  Many thanks!!

						- Ted

[09:35:46] ==================== test_mb_mark_used  ====================
[09:35:46] [ERROR] Test: test_mb_mark_used: missing subtest result line!
[09:35:46] 
[09:35:46] Pid: 35, comm: kunit_try_catch Tainted: G        W        N  6.16.0-rc4-00031-gbbe11dd13a3f-dirty
[09:35:46] RIP: 0033:mb_set_largest_free_order+0x5c/0xc0
[09:35:46] RSP: 00000000a0883d98  EFLAGS: 00010206
[09:35:46] RAX: 0000000060aeaa28 RBX: 0000000060a2d400 RCX: 0000000000000008
[09:35:46] RDX: 0000000060aea9c0 RSI: 0000000000000000 RDI: 0000000060864000
[09:35:46] RBP: 0000000060aea9c0 R08: 0000000000000000 R09: 0000000060a2d400
[09:35:46] R10: 0000000000000400 R11: 0000000060a9cc00 R12: 0000000000000006
[09:35:46] R13: 0000000000000400 R14: 0000000000000305 R15: 0000000000000000
[09:35:46] Kernel panic - not syncing: Segfault with no mm
[09:35:46] CPU: 0 UID: 0 PID: 35 Comm: kunit_try_catch Tainted: G        W        N  6.16.0-rc4-00031-gbbe11dd13a3f-dirty #36 NONE
[09:35:46] Tainted: [W]=WARN, [N]=TEST
[09:35:46] Stack:
[09:35:46]  60210c60 00000200 60a9e400 00000400
[09:35:46]  40060300280 60864000 60a9cc00 60a2d400
[09:35:46]  00000400 60aea9c0 60a9cc00 60aea9c0
[09:35:46] Call Trace:
[09:35:46]  [<60210c60>] ? ext4_mb_generate_buddy+0x1f0/0x230
[09:35:46]  [<60215c3b>] ? test_mb_mark_used+0x28b/0x4e0
[09:35:46]  [<601df5bc>] ? ext4_get_group_desc+0xbc/0x150
[09:35:46]  [<600bf1c0>] ? ktime_get_ts64+0x0/0x190
[09:35:46]  [<60086370>] ? to_kthread+0x0/0x40
[09:35:46]  [<602b559b>] ? kunit_try_run_case+0x7b/0x100
[09:35:46]  [<60086370>] ? to_kthread+0x0/0x40
[09:35:46]  [<602b7850>] ? kunit_generic_run_threadfn_adapter+0x0/0x30
[09:35:46]  [<602b7862>] ? kunit_generic_run_threadfn_adapter+0x12/0x30
[09:35:46]  [<60086a51>] ? kthread+0xf1/0x250
[09:35:46]  [<6004a541>] ? new_thread_handler+0x41/0x60
[09:35:46] [ERROR] Test: test_mb_mark_used: 0 tests run!
[09:35:46] ============= [NO TESTS RUN] test_mb_mark_used =============