linux-kernel - Re: [PATCH v5] x86/split_lock: fix delayed detection enabling

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Message-ID: <Z9seaRFmQ9nlOlWf@gmail.com>
Date: Wed, 19 Mar 2025 20:43:37 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Maksim Davydov <davydov-max@...dex-team.ru>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	den-plotnikov@...dex-team.ru, gpiccoli@...lia.com, mingo@...hat.com,
	bp@...en8.de, dave.hansen@...ux.intel.com, tglx@...utronix.de,
	hpa@...or.com
Subject: Re: [PATCH v5] x86/split_lock: fix delayed detection enabling


* Maksim Davydov <davydov-max@...dex-team.ru> wrote:

> 
> 
> On 3/18/25 23:24, Ingo Molnar wrote:
> > 
> > * Maksim Davydov <davydov-max@...dex-team.ru> wrote:
> > 
> > > If the warn mode with disabled mitigation mode is used, then on each
> > > CPU where the split lock occurred detection will be disabled in order to
> > > make progress and delayed work will be scheduled, which then will enable
> > > detection back. Now it turns out that all CPUs use one global delayed
> > > work structure. This leads to the fact that if a split lock occurs on
> > > several CPUs at the same time (within 2 jiffies), only one CPU will
> > > schedule delayed work, but the rest will not. The return value of
> > > schedule_delayed_work_on() would have shown this, but it is not checked
> > > in the code.
> > 
> > So we already merged the previous version into the locking tree ~10
> > days ago and it's all in -next already:
> > 
> >    c929d08df8be ("x86/split_lock: Fix the delayed detection logic")
> > 
> >    https://web.git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=c929d08df8bee855528b9d15b853c892c54e1eee
> > 
> > Is there anything new in your -v5 patch, other than undoing all the
> > changelog cleanups I did for the previous version? ;-)
> > 
> 
> Oh, sorry, I missed it.
> Yes, in v5 initcall is used instead of deferred initialization.
> Either v4 or v5 are good for me. Please be free to choose the more
> convenient variant for you. :-)

Could you please send a delta patch on top of tip:master (or -next) 
that implements the initcall approach? Basically -v5, but on top of 
-v4.

I merged -v4 because I thought the fix was delayed enough already and 
-v4 was functionally fine too, but I won't say no to even better code! :-)

Thanks,

	Ingo