linux-kernel - Re: [PATCH RFC v2 03/10] locking/local_lock: Introduce localtry_lock

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Message-ID: <CAADnVQLAfZBvSyqE=2sbdH-kuNhvAJM+R_qMzfgPv=MDF+=VQA@mail.gmail.com>
Date: Wed, 26 Feb 2025 09:15:10 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Vlastimil Babka <vbabka@...e.cz>, Suren Baghdasaryan <surenb@...gle.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Christoph Lameter <cl@...ux.com>, 
	David Rientjes <rientjes@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Hyeonggon Yoo <42.hyeyoo@...il.com>, Uladzislau Rezki <urezki@...il.com>, linux-mm <linux-mm@...ck.org>, 
	LKML <linux-kernel@...r.kernel.org>, rcu@...r.kernel.org, 
	maple-tree@...ts.infradead.org, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH RFC v2 03/10] locking/local_lock: Introduce localtry_lock_t

On Wed, Feb 26, 2025 at 9:01 AM Davidlohr Bueso <dave@...olabs.net> wrote:
>
> On Fri, 14 Feb 2025, Vlastimil Babka wrote:
>
> >From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> >
> >In !PREEMPT_RT local_lock_irqsave() disables interrupts to protect
> >critical section, but it doesn't prevent NMI, so the fully reentrant
> >code cannot use local_lock_irqsave() for exclusive access.
> >
> >Introduce localtry_lock_t and localtry_lock_irqsave() that
> >disables interrupts and sets acquired=1, so localtry_lock_irqsave()
> >from NMI attempting to acquire the same lock will return false.
> >
> >In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
> >Map localtry_lock_irqsave() to preemptible spin_trylock().
> >When in hard IRQ or NMI return false right away, since
> >spin_trylock() is not safe due to PI issues.
> >
> >Note there is no need to use local_inc for acquired variable,
> >since it's a percpu variable with strict nesting scopes.
> >
>
> LGTM.
>
> Acked-by: Davidlohr Bueso <dave@...olabs.net>

Thanks for the review.
Do you mind if I apply your ack to the latest version of this patch?
https://lore.kernel.org/bpf/20250222024427.30294-2-alexei.starovoitov@gmail.com/