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 C406E471260; Tue, 21 Jul 2026 21:08:46 +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=1784668127; cv=none; b=pDkBEuy+neJ69ujBKU96elVdoq0+G7WC38Aat1NVw/dmDyLfm5nI8l5BHJu66GeXc5GYM89RLuZbJQrirK7flLYnx8C+2SFf957V6etLXdrEN+whaMFWfZrkORxXXP6400uNtsXNaeMosno59GQN9bsDd+IoZGbJw6xJGtlXCbI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784668127; c=relaxed/simple; bh=zdEk9GdO0PG27bHN2ZqsXVIW/BE5AxeE4h41HzKzknU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=sJqN1L6bVhWNbrnnQsRNhb+DZGAbfeAIeHUdHDmPhqNjWKhfqD2YqcoI+B0dA13eQgM6df4ShrX0EK3Y7mgj7Mj3Z70TsBUc/QxNKpahkbDqO39MY5pDqqCtgvwjwiVXbiC6vIKFE+0GJ/FqwAtZtCszXPILc+MJVD8CW4i2fbg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=WahoVUBA; 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="WahoVUBA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E9F41F000E9; Tue, 21 Jul 2026 21:08:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784668126; bh=blctjwWlsQSJnhcPeTyMnW6+c2105Q+CpXpejBlW93U=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=WahoVUBAvKOzxsU9exPWZ/tl02Rm7ZUN/RE4VQ+QLnlZ5eap87GvibFhFKE54+rYG Ef917nDs7+ZT+G1iIDnjCE+ImW7C/VrU9o0S/ii1CZZeH1K4H2ATx/pTYIYjDjgRqh Qu/VNYKZW75SSVsCwn15/VMOViu6iLDxDR6GpvLY= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Huacai Chen , Sasha Levin Subject: [PATCH 6.1 0005/1067] LoongArch: Report dying CPU to RCU in stop_this_cpu() Date: Tue, 21 Jul 2026 17:10:06 +0200 Message-ID: <20260721152424.653009215@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152424.521567757@linuxfoundation.org> References: <20260721152424.521567757@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 6.1-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 18a2b37f4aea37..356918d5aa28f1 100644 --- a/arch/loongarch/kernel/smp.c +++ b/arch/loongarch/kernel/smp.c @@ -517,6 +517,7 @@ 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