linux-kernel - Re: [syzbot] [cgroups?] possible deadlock in __run_timer

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Message-ID: <812ea88a-b79e-49e0-ab3b-83cd40b2851e@redhat.com>
Date: Fri, 14 Feb 2025 09:17:35 -0500
From: Waiman Long <llong@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>, Waiman Long <llong@...hat.com>
Cc: syzbot <syzbot+ed801a886dfdbfe7136d@...kaller.appspotmail.com>,
 cgroups@...r.kernel.org, hannes@...xchg.org, linux-kernel@...r.kernel.org,
 mkoutny@...e.com, syzkaller-bugs@...glegroups.com, tj@...nel.org
Subject: Re: [syzbot] [cgroups?] possible deadlock in __run_timer_base (2)


On 2/14/25 5:19 AM, Peter Zijlstra wrote:
> On Tue, Feb 11, 2025 at 09:14:12PM -0500, Waiman Long wrote:
>> On 2/9/25 3:43 PM, syzbot wrote:
>>> Hello,
>>>
>>> syzbot found the following issue on:
>>>
>>> HEAD commit:    92514ef226f5 Merge tag 'for-6.14-rc1-tag' of git://git.ker..
>>> git tree:       upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=179453df980000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=1909f2f0d8e641ce
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=ed801a886dfdbfe7136d
>>> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>>>
>>> Unfortunately, I don't have any reproducer for this issue yet.
>>>
>>> Downloadable assets:
>>> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-92514ef2.raw.xz
>>> vmlinux: https://storage.googleapis.com/syzbot-assets/c4d8b91f8769/vmlinux-92514ef2.xz
>>> kernel image: https://storage.googleapis.com/syzbot-assets/c24ec4365966/bzImage-92514ef2.xz
>>>
>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>> Reported-by: syzbot+ed801a886dfdbfe7136d@...kaller.appspotmail.com
>> This problem should be fixed by the following upstream patch once it is
>> merged into mainline.
>>
>> https://lore.kernel.org/lkml/20250127013127.3913153-1-longman@redhat.com/
>>
> AFAICT all these lockdep reports are because of an earlier warning. Fix
> warning, report goes away. Notably:
>
>>>          _printk+0xd5/0x120 kernel/printk/printk.c:2457
>>>          __report_bug lib/bug.c:195 [inline]
>>>          report_bug+0x346/0x500 lib/bug.c:219
>>>          handle_bug+0x60/0x90 arch/x86/kernel/traps.c:285
>>>          exc_invalid_op+0x1a/0x50 arch/x86/kernel/traps.c:309
>>>          asm_exc_invalid_op+0x1a/0x20 arch/x86/include/asm/idtentry.h:621
>>>          expire_timers kernel/time/timer.c:1827 [inline]
> IOW I think we're focusing on the wrong thing here.
>
>> Peter, are you planning to merge this patch? This is another instance where
>> the old way of calling wake_up_process() inside the lock critical region can
>> lead to deadlock.
> I still don't love the Changelog, but yeah, I suppose I can pick it up.
> But I see Boqun took it and I'll get it eventually.
>
> No real hurry there I suppose.

I know my changelog is sometimes too verbose and may contain 
non-important information. I will try to improve that in the future.

Cheers,
Longman

>