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From: "Chuyi Zhou" <zhouchuyi@bytedance.com>
To: "Peter Zijlstra" <peterz@infradead.org>
Cc: <tglx@linutronix.de>, <mingo@redhat.com>, <luto@kernel.org>,
	 <paulmck@kernel.org>, <muchun.song@linux.dev>, <bp@alien8.de>,
	 <dave.hansen@linux.intel.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 05/11] smp: Enable preemption early in smp_call_function_many_cond
Date: Mon, 9 Feb 2026 15:56:23 +0800	[thread overview]
Message-ID: <3f474d49-bf07-4a2c-aa38-093373bd5bf5@bytedance.com> (raw)
In-Reply-To: <20260205095236.GI232055@noisy.programming.kicks-ass.net>

在 2026/2/5 17:52, Peter Zijlstra 写道:
> 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.



Here we can use rcu_read_lock to replace migrate_disable/cpus_read_lock, 
and in smpcfd_dead_cpu(), wait for all rcu read critical sections to 
exit before releasing percpu csd data.

This allows csd_lock_wait() to be preemptible and migratable, while 
avoiding concurrency issues between smpcfd_dead_cpu() and csd_lock_wait.

Thanks.

  parent reply	other threads:[~2026-02-09  7:56 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-02-03 11:23 [PATCH 00/11] Allow preemption during IPI completion waiting to improve real-time performance Chuyi Zhou
2026-02-03 11:23 ` [PATCH 01/11] smp: Disable preemption explicitly in __csd_lock_wait Chuyi Zhou
2026-02-05  6:05   ` Muchun Song
2026-02-03 11:23 ` [PATCH 02/11] smp: Enable preemption early in smp_call_function_single Chuyi Zhou
2026-02-05  3:55   ` Muchun Song
2026-02-05  9:34   ` Peter Zijlstra
2026-02-03 11:23 ` [PATCH 03/11] smp: Remove get_cpu from smp_call_function_any Chuyi Zhou
2026-02-05  6:03   ` Muchun Song
2026-02-05  9:42   ` Peter Zijlstra
2026-02-06  8:54     ` Chuyi Zhou
2026-02-03 11:23 ` [PATCH 04/11] smp: Use on-stack cpumask in smp_call_function_many_cond Chuyi Zhou
2026-02-05  9:44   ` Peter Zijlstra
2026-02-06  9:07     ` Chuyi Zhou
2026-02-05  9:51   ` Peter Zijlstra
2026-02-03 11:23 ` [PATCH 05/11] smp: Enable preemption early " Chuyi Zhou
2026-02-05  9:52   ` Peter Zijlstra
2026-02-05 10:57     ` Peter Zijlstra
2026-02-05 14:29       ` Chuyi Zhou
2026-02-05 14:59         ` Peter Zijlstra
2026-02-06  8:43           ` Chuyi Zhou
2026-02-06  9:47             ` Peter Zijlstra
2026-02-06 11:45               ` Chuyi Zhou
2026-02-09  7:56     ` Chuyi Zhou [this message]
2026-02-03 11:23 ` [PATCH 06/11] smp: Remove preempt_disable from smp_call_function Chuyi Zhou
2026-02-03 11:23 ` [PATCH 07/11] smp: Remove preempt_disable from on_each_cpu_cond_mask Chuyi Zhou
2026-02-03 11:23 ` [PATCH 08/11] scftorture: Remove preempt_disable in scftorture_invoke_one Chuyi Zhou
2026-02-03 11:23 ` [PATCH 09/11] x86/mm: Move flush_tlb_info back to the stack Chuyi Zhou
2026-02-03 11:24 ` [PATCH 10/11] x86/mm: Enable preemption during native_flush_tlb_multi Chuyi Zhou
2026-02-03 11:24 ` [PATCH 11/11] x86/mm: Enable preemption during flush_tlb_kernel_range Chuyi Zhou

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