linux-kernel - Re: [PATCH RESEND] x86/split_lock: Warn for bus locks once for each task

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Message-ID: <f41505e6-62da-480c-86ed-5eccd309cc2d@yandex-team.ru>
Date: Thu, 2 Oct 2025 15:57:46 +0300
From: Maksim Davydov <davydov-max@...dex-team.ru>
To: Pedro Falcato <pfalcato@...e.de>
Cc: "H. Peter Anvin" <hpa@...or.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Subject: Re: [PATCH RESEND] x86/split_lock: Warn for bus locks once for each
 task

On 9/17/25 18:37, Pedro Falcato wrote:
> On Wed, Sep 17, 2025 at 05:41:11PM +0300, Maksim Davydov wrote:
>> Hi!
> 
> Hi!
> 
>> I've tested this patch (VM w/ bus lock detection and w/o split lock
>> detection). The warn mode works fine and as expected with only one
>> notification per task. However, the ratelimit mode has been changed too:
>> only one notification per task will be in dmesg, because this mode reuses
>> notification code of warn mode. But in the documentation for ratelimit mode
>> there is nothing about the limit of notifications: "Limit bus lock rate to N
>> bus locks per second system wide and warn on bus locks.". Thus, I think that
>> ratelimit mode should remain old behaviour.
>>
> 
> So, you're suggesting different "warn" behaviors depending on =warn vs
> =ratelimit? I don't have a particularly strong opinion here, but I was assuming
> that "warn on bus locks" means "do whatever =warn is supposed to do". I'm not
> sure warning every time gains you much, though.
> 

For me, it's ok to reduce the number of messages to one per task.

By the way, I read the patch again and noticed that split_lock_warn() 
and handle_bus_lock() print messages in the same way. Maybe, it'll be 
better to implement an auxiliary wrapper for printing 
split_lock/bus_lock warning messages (for example, 
print_sl_warn_once()), what do you think?

-- 
Best regards,
Maksim Davydov