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

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Message-ID: <20250226170053.lxpreaegz5tysef7@offworld>
Date: Wed, 26 Feb 2025 09:00:53 -0800
From: Davidlohr Bueso <dave@...olabs.net>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: 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@...ck.org,
	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 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>