linux-kernel - Re: [PATCH bpf-next v1 08/22] rqspinlock: Protect pending bit owners from stalls

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Message-ID: <20250107145159.GB23315@noisy.programming.kicks-ass.net>
Date: Tue, 7 Jan 2025 15:51:59 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
	Barret Rhoden <brho@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Waiman Long <llong@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>, Tejun Heo <tj@...nel.org>,
	Josh Don <joshdon@...gle.com>, Dohyun Kim <dohyunkim@...gle.com>,
	kernel-team@...a.com
Subject: Re: [PATCH bpf-next v1 08/22] rqspinlock: Protect pending bit owners
 from stalls

On Tue, Jan 07, 2025 at 05:59:50AM -0800, Kumar Kartikeya Dwivedi wrote:
> +	if (val & _Q_LOCKED_MASK) {
> +		RES_RESET_TIMEOUT(ts);
> +		smp_cond_load_acquire(&lock->locked, !VAL || RES_CHECK_TIMEOUT(ts, ret));
> +	}

Please check how smp_cond_load_acquire() works on ARM64 and then add
some words on how RES_CHECK_TIMEOUT() is still okay.