[syzbot] [kernel?] linux-next test error: WARNING in class_for_each_device

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d387b06f7c15 Add linux-next specific files for 20260525
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15eb7796580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8dd72cf810e753a6
dashboard link: https://syzkaller.appspot.com/bug?extid=50b5f81fff158669504a
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/39490dfbc250/disk-d387b06f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0789ac7ac5fc/vmlinux-d387b06f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4464df9f5ccf/bzImage-d387b06f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+50b5f8...@syzkaller.appspotmail.com

------------[ cut here ]------------
class_for_each_device called for class 'devlink' before it was registered
WARNING: drivers/base/class.c:416 at class_for_each_device+0x2d8/0x390 drivers/base/class.c:415, CPU#1: kworker/1:1/37
Modules linked in:
CPU: 1 UID: 0 PID: 37 Comm: kworker/1:1 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: events deferred_probe_timeout_work_func
RIP: 0010:class_for_each_device+0x2fc/0x390 drivers/base/class.c:415
Code: 8d 1d 38 5c 0e 0a 4c 89 e8 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 ef e8 62 fc a5 fc 49 8b 55 00 48 89 df 48 c7 c6 f1 46 5d 8d <67> 48 0f b9 3a b8 ea ff ff ff eb 1b e8 93 79 3b fc 49 81 c6 90 00
RSP: 0000:ffffc90000ac7a20 EFLAGS: 00010246
RAX: 1ffffffff17865d4 RBX: ffffffff8f984790 RCX: ffff88801e2e9f00
RDX: ffffffff8bc34360 RSI: ffffffff8d5d46f1 RDI: ffffffff8f984790
RBP: ffffc90000ac7af8 R08: ffffc90000ac7a7f R09: 0000000000000000
R10: ffffc90000ac7a60 R11: fffff52000158f50 R12: ffffc90000ac7a60
R13: ffffffff8bc32ea0 R14: 1ffff92000158f48 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff888125fdb000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000000ddb8000 CR4: 00000000003506f0
Call Trace:
<TASK>
fw_devlink_drivers_done+0x35/0x50 drivers/base/core.c:1837
deferred_probe_timeout_work_func+0x21/0x220 drivers/base/dd.c:305
process_one_work+0x98b/0x1630 kernel/workqueue.c:3318
process_scheduled_works kernel/workqueue.c:3401 [inline]
worker_thread+0xb49/0x1140 kernel/workqueue.c:3482
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
----------------
Code disassembly (best guess):
0: 8d 1d 38 5c 0e 0a lea 0xa0e5c38(%rip),%ebx # 0xa0e5c3e
6: 4c 89 e8 mov %r13,%rax
9: 48 c1 e8 03 shr $0x3,%rax
d: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1)
12: 74 08 je 0x1c
14: 4c 89 ef mov %r13,%rdi
17: e8 62 fc a5 fc call 0xfca5fc7e
1c: 49 8b 55 00 mov 0x0(%r13),%rdx
20: 48 89 df mov %rbx,%rdi
23: 48 c7 c6 f1 46 5d 8d mov $0xffffffff8d5d46f1,%rsi
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: b8 ea ff ff ff mov $0xffffffea,%eax
34: eb 1b jmp 0x51
36: e8 93 79 3b fc call 0xfc3b79ce
3b: 49 rex.WB
3c: 81 .byte 0x81
3d: c6 (bad)
3e: 90 nop


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[Tetsuo Handa]

On 2026/05/26 14:55, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: d387b06f7c15 Add linux-next specific files for 20260525
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=15eb7796580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=8dd72cf810e753a6
> dashboard link: https://syzkaller.appspot.com/bug?extid=50b5f81fff158669504a
> compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/39490dfbc250/disk-d387b06f.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/0789ac7ac5fc/vmlinux-d387b06f.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/4464df9f5ccf/bzImage-d387b06f.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+50b5f8...@syzkaller.appspotmail.com
>
> ------------[ cut here ]------------
> class_for_each_device called for class 'devlink' before it was registered

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/base?id=1137838865bfc9a7cd5869c1dc5c22aa45ec12c8

Why "driver_deferred_probe_timeout * HZ" => "driver_deferred_probe_timeout" ?

[Tetsuo Handa]

Here is an analysis from Google AI mode regarding this problem: https://share.google/aimode/UO1WnoKPDSbyjY5Qj

Greg, can you immediately drop commit 1137838865bf ("driver core: Use mod_delayed_work to prevent
lost deferred probe work") so that syzbot can resume testing linux-next tree as soon as possible?

[Tetsuo Handa]

Below diff was generated via conversation with AI Mode in Google Search, and
I agree that this diff should fix the problem. I'm waiting for Greg's response
on how to proceed. Mark, can you carry below diff as a hotfix for linux-next tree?

---
drivers/base/dd.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 172a02a438a2..265717a19b08 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -298,10 +298,14 @@ int driver_deferred_probe_check_state(struct device *dev)
}
EXPORT_SYMBOL_GPL(driver_deferred_probe_check_state);

+static int deferred_probe_timeout_triggered __data_racy;
static void deferred_probe_timeout_work_func(struct work_struct *work)
{
struct device_private *p;

+ if (cmpxchg(&deferred_probe_timeout_triggered, 0, 1))
+ return;
+
fw_devlink_drivers_done();

driver_deferred_probe_timeout = 0;
@@ -323,8 +327,9 @@ void deferred_probe_extend_timeout(void)
* If the work hasn't been queued yet or if the work expired, don't
* start a new one.
*/
- if (mod_delayed_work(system_wq, &deferred_probe_timeout_work,
- driver_deferred_probe_timeout))
+ if (!deferred_probe_timeout_triggered &&
+ mod_delayed_work(system_wq, &deferred_probe_timeout_work,
+ driver_deferred_probe_timeout * HZ))
pr_debug("Extended deferred probe timeout by %d secs\n",
driver_deferred_probe_timeout);
}
@@ -357,10 +362,11 @@ static int deferred_probe_initcall(void)
driver_deferred_probe_trigger();
flush_work(&deferred_probe_work);

- if (driver_deferred_probe_timeout > 0) {
+ if (driver_deferred_probe_timeout > 0)
schedule_delayed_work(&deferred_probe_timeout_work,
driver_deferred_probe_timeout * HZ);
- }
+ else
+ deferred_probe_timeout_triggered = 1;

if (!IS_ENABLED(CONFIG_MODULES))
fw_devlink_probing_done();
--
2.54.0

[Danilo Krummrich]

I already posted patches to fix this in [1]. I will pick them up today.

[1] https://lore.kernel.org/driver-core/20260525012340...@kernel.org/t/#u

[Danilo Krummrich]

As mentioned in the previous reply, I already posted patches for this in [1];