linux-kernel - Re: [PATCH 05/11] smp: Enable preemption early in smp_call_function_many

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Message-ID: <20260205095236.GI232055@noisy.programming.kicks-ass.net>
Date: Thu, 5 Feb 2026 10:52:36 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Chuyi Zhou <zhouchuyi@...edance.com>
Cc: tglx@...utronix.de, mingo@...hat.com, luto@...nel.org,
	paulmck@...nel.org, muchun.song@...ux.dev, bp@...en8.de,
	dave.hansen@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/11] smp: Enable preemption early in
 smp_call_function_many_cond

On Tue, Feb 03, 2026 at 07:23:55PM +0800, Chuyi Zhou wrote:

> +	/*
> +	 * Prevent the current CPU from going offline.
> +	 * Being migrated to another CPU and calling csd_lock_wait() may cause
> +	 * UAF due to smpcfd_dead_cpu() during the current CPU offline process.
> +	 */
> +	migrate_disable();

This is horrible crap. migrate_disable() is *NOT* supposed to be used to
serialize cpu hotplug.