linux-kernel - Re: [PATCH] percpu: fix race on alloc failed warning limit

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Message-ID: <061405e5-8670-2873-9b6f-0f152863adfc@gentwo.org>
Date: Tue, 2 Sep 2025 10:39:54 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Vlad Dumitrescu <vdumitrescu@...dia.com>
cc: Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, 
    Baoquan He <bhe@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, 
    linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] percpu: fix race on alloc failed warning limit

On Fri, 22 Aug 2025, Vlad Dumitrescu wrote:

> +	if (do_warn && atomic_read(&warn_limit) > 0) {
> +		int remaining = atomic_dec_return(&warn_limit);


The code creates a race condition since another atomic_dec_return() can
happen on another cpu between these two lines. warn_limit can go negative.

Use a single atomic operation instead?