From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D9A81414A27; Tue, 21 Jul 2026 20:11:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784664692; cv=none; b=pQ6IwcPpFoNuZrkQ0+4J5Bh03UZs5y0GGXXigs0C/RJD9ASFOqUHcznxTOM4/AQG/z52oNauYjZIVCC7km5ZML8KY1UdwNh1++LyWUfXvoZo9ds3qX1C4mQXaCCp0dX7pagjW3oyK1HNm8fFsIlHG5SIIJJErzrakkEQRf78s04= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784664692; c=relaxed/simple; bh=IWwsFIGLuq0LdUFFmMimbsO0doJ9pKuJiQt+rDcsYXI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=qxB5OogJ4YBN7QPGDSdrOXEbpUBJQj994h1LXjCnMZwdSW+ZCMbTsKAMqzrjQTSVSu/NhvH6wmNt5ToTgzkFFKKNzeUxw/m3y53J2C8ef63DzwZo7ZCSlGCYpRM4gN3Sa3Yu/x5l8nQ+PPDsTP4UrKth4NRhVkTk9YrGM2iR72I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=rwFboxS5; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="rwFboxS5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 726681F000E9; Tue, 21 Jul 2026 20:11:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784664690; bh=Yotbll1DZ7ykUzK6oYyqfcVTh5HJ5QPtWhse/1hMiHE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=rwFboxS5gMCmPtxfXkpHRNGtgb7Mt4bYSKDJ8VqJfWTixkQVM+ssOo7t4Ye9EFUsJ Oqpk/9jEL5AJPPcmanNnxqNqujNhhfQlmr/Zemz6GiIMUlZt1QJa/AdrbhWg8a/Sng 1RlZulWqAVzCzmOj07bmYLI/BkWmDXzYi7wTDgt4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Huacai Chen , Sasha Levin Subject: [PATCH 6.6 0005/1266] LoongArch: Report dying CPU to RCU in stop_this_cpu() Date: Tue, 21 Jul 2026 17:07:22 +0200 Message-ID: <20260721152441.912571268@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152441.786066624@linuxfoundation.org> References: <20260721152441.786066624@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Huacai Chen commit f2539c56c74691e7a88af6372ba2b48c06ed2fe4 upstream. This is a port of MIPS commit 9f3f3bdc6d9dac1 ("MIPS: smp: report dying CPU to RCU in stop_this_cpu()"). smp_send_stop() parks all secondary CPUs in stop_this_cpu(). And the function marks the CPU offline for the scheduler via set_cpu_online(false) but never informs RCU, so RCU keeps expecting a quiescent state from CPUs that are now spinning forever with interrupts disabled. As long as nothing waits for an RCU grace period after smp_send_stop() this is harmless, which is why it went unnoticed. However, since commit 91840be8f710370 ("irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT"), irq_work_sync() calls synchronize_rcu() on architectures without an irq_work self-IPI, i.e. where arch_irq_work_has_interrupt() returns false. Any irq_work_sync() issued in the reboot/shutdown/halt path after smp_send_stop() then blocks on a grace period that can never complete, hanging the reboot: WARNING: CPU: 0 PID: 15 at kernel/irq_work.c:144 irq_work_queue_on ... rcu: INFO: rcu_sched detected stalls on CPUs/tasks: rcu: Offline CPU 1 blocking current GP. rcu: Offline CPU 2 blocking current GP. rcu: Offline CPU 3 blocking current GP. This issue needs some hacks to reproduce, and it was not noticed on LoongArch because arch_irq_work_has_interrupt() usually returns true. Call rcutree_report_cpu_dead() once interrupts are disabled, mirroring the generic CPU-hotplug offline path, so RCU stops waiting on the parked CPUs and grace periods can still complete. LoongArch shuts down all CPUs here without going through the CPU-hotplug mechanism, so this report is not otherwise issued. Cc: Fixes: 91840be8f710 ("irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT") Signed-off-by: Huacai Chen Signed-off-by: Sasha Levin --- arch/loongarch/kernel/smp.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c index ed67629454374f..d3fafa5cdf6bc8 100644 --- a/arch/loongarch/kernel/smp.c +++ b/arch/loongarch/kernel/smp.c @@ -613,6 +613,7 @@ static void stop_this_cpu(void *dummy) set_cpu_online(smp_processor_id(), false); calculate_cpu_foreign_map(); local_irq_disable(); + rcu_report_dead(smp_processor_id()); while (true); } -- 2.53.0