Subject: Re: commit dd4cf8c9e1f4 leads to failed boot

From: "Aithal, Srikanth" <[email-masked]>
Date: Thu, 24 Apr 2025 10:00:36 +0530

On 4/24/2025 1:26 AM, Paul E. McKenney wrote:
> On Wed, Apr 23, 2025 at 09:19:56PM +0200, Bert Karwatzki wrote:
>> Am Mittwoch, dem 23.04.2025 um 11:07 -0700 schrieb Paul E. McKenney:
>>> On Wed, Apr 23, 2025 at 08:49:08PM +0530, Aithal, Srikanth wrote:
>>>> On 4/23/2025 7:48 PM, Paul E. McKenney wrote:
>>>>> On Wed, Apr 23, 2025 at 07:09:42PM +0530, Aithal, Srikanth wrote:
>>>>>> On 4/23/2025 5:24 PM, Bert Karwatzki wrote:
>>>>>>> Since linux next-20250422 booting fails on my MSI Alpha 15 Laptop runnning
>>>>>>> debian sid. When booting kernel message appear on screen but no messages from
>>>>>>> init (systemd). There are also no logs written even thought emergency sync
>>>>>>> via magic sysrq works (a message is printed on screen), presumably because
>>>>>>> / is not mounted. I bisected this (from 6.15-rc3 to next-20250422) and found
>>>>>>> commit dd4cf8c9e1f4 as the first bad commit.
>>>>>>> Reverting commit dd4cf8c9e1f4 in next-20250422 fixes the issue.
>>>>>>
>>>>>>
>>>>>> Hello,
>>>>>>
>>>>>> On AMD platform as well boot failed starting next-20250422, bisecting the
>>>>>> issue led me to same commit dd4cf8c9e1f4. I have attached kernel config and
>>>>>> logs.
>>>>>
>>>>> Thank you all for the bisection and the report!
>>>>>
>>>>> Please check out the predecessor of commit dd4cf8c9e1f4 ("ratelimit:
>>>>> Force re-initialization when rate-limiting re-enabled"):
>>>>>
>>>>> 13fa70e052dd ("ratelimit: Allow zero ->burst to disable ratelimiting")
>>>>>
>>>>> Then please apply the patch shown below, and let me know what happens?
>>>>> (Yes, I should have split that commit up...)
>>>>>
>>>>> 							Thanx, Paul
>>>>>
>>>>> ------------------------------------------------------------------------
>>>>>
>>>>> diff --git a/lib/ratelimit.c b/lib/ratelimit.c
>>>>> index 04f16b8e24575..13ed636642270 100644
>>>>> --- a/lib/ratelimit.c
>>>>> +++ b/lib/ratelimit.c
>>>>> @@ -35,7 +35,7 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
>>>>>    	unsigned long flags;
>>>>>    	int ret;
>>>>> -	if (!interval || !burst)
>>>>> +	if (interval <= 0 || burst <= 0)
>>>>>    		return 1;
>>>>>    	/*
>>>>
>>>>
>>>> I applied above patch on top of 13fa70e052dd ("ratelimit: Allow zero ->burst
>>>> to disable ratelimiting") [linux-20250423]. This is fixing the boot issue.
>>>>
>>>> Tested-by: Srikanth Aithal <[email-masked]>
>>>
>>> Thank you both, and to Bert for intuiting the correct -next commit!
>>>
>>> Could you please try the next increment, which is this patch, again
>>> on top of 24ff89c63355 ("ratelimit: Allow zero ->burst to > disable
>>> ratelimiting")?
>>>
>>> In the meantime, I will expose the version you two just tested to
>>> -next.
>>>
>>> 							Thanx, Paul
>>>
>>> ------------------------------------------------------------------------
>>>
>>> diff --git a/lib/ratelimit.c b/lib/ratelimit.c
>>> index 04f16b8e24575..8f6c54f719ef2 100644
>>> --- a/lib/ratelimit.c
>>> +++ b/lib/ratelimit.c
>>> @@ -35,8 +35,10 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
>>>   	unsigned long flags;
>>>   	int ret;
>>>   
>>> -	if (!interval || !burst)
>>> +	if (interval <= 0 || burst <= 0) {
>>> +		ret = burst > 0;
>>>   		return 1;
>>> +	}
>>>   
>>>   	/*
>>>   	 * If we contend on this state's lock then just check if
>>
>> If you set "ret = burst > 0", but "return 1" this will make no difference
>> (except in the case of a major compiler bug, probably), as I wrote in my other
>> email which overlapped yours, this fixes the issue in next-20250422:
>>
>> diff --git a/lib/ratelimit.c b/lib/ratelimit.c
>> index b5c727e976d2..fc28f6cf8269 100644
>> --- a/lib/ratelimit.c
>> +++ b/lib/ratelimit.c
>> @@ -40,7 +40,7 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
>>           * interval says never limit.
>>           */
>>          if (interval <= 0 || burst <= 0) {
>> -               ret = burst > 0;
>> +               ret = 1;
>>                  if (!(READ_ONCE(rs->flags) & RATELIMIT_INITIALIZED) ||
>>                      !raw_spin_trylock_irqsave(&rs->lock, flags))
>>                          return ret;
> 
> You are quite right, your patch does fix the issue that you three say.
> Unfortunately, it prevents someone from completely suppressing output
> by setting burst to zero.  Could you please try the patch below?
> 
> 							Thanx, Paul

I have tested the below patch on top of 13fa70e052dd ("ratelimit: Allow 
zero ->burst to disable ratelimiting") [linux-20250423].
This is fixing the boot issue. Thanks again!

Tested-by: Srikanth Aithal <[email-masked]>

> 
> ------------------------------------------------------------------------
> 
> diff --git a/lib/ratelimit.c b/lib/ratelimit.c
> index 04f16b8e24575..d6531e5c6ec4e 100644
> --- a/lib/ratelimit.c
> +++ b/lib/ratelimit.c
> @@ -35,8 +35,8 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
>   	unsigned long flags;
>   	int ret;
>   
> -	if (!interval || !burst)
> -		return 1;
> +	if (interval <= 0 || burst <= 0)
> +		return interval == 0 || burst > 0;
>   
>   	/*
>   	 * If we contend on this state's lock then just check if