From nobody Wed Dec 17 09:18:31 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3BEDBEE49A3 for ; Tue, 22 Aug 2023 09:01:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234145AbjHVJBe (ORCPT ); Tue, 22 Aug 2023 05:01:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36348 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234140AbjHVJBc (ORCPT ); Tue, 22 Aug 2023 05:01:32 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9DC851B2; Tue, 22 Aug 2023 02:01:30 -0700 (PDT) Received: from localhost.localdomain (unknown [39.45.215.81]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id 61634660723E; Tue, 22 Aug 2023 10:01:27 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1692694889; bh=G+PYlsLKKNrAJfjnLhUkS/SXCH0SH1cJtUJtNZ50U6Q=; h=From:To:Cc:Subject:Date:From; b=kGi7C/fwaHu5a8ZX9E0xrhwivYmQ9nFQV2i0aRhf5Ag1tBQKCdVCQ8QWyuBfMLDGJ vellhOLG+C48tk8dXJIaNGg72aRZIMQEkcAtPe/aadZFvs5Z8EcyI37HGIfgu0fmq2 z4c+q2LjoTk0VX4ATRzVZ7YFGvyXwTMSvN3MRiHE2RKw1688gsYj2xOL7dibahaPJS F+Thb9u6OnMLND1UZWr0mbOB7+DEUu/j7mF4C4r8HOMDhwxj+Ps5STxKK4zM+0UYyX guQUetONQwfdps0WvR0oIwMC4nu2k99uWU1kVjqXknY0odpUoSgp4HUOUAcNfI/kWS VQhWpiTqpYAnQ== From: Muhammad Usama Anjum To: Greg Kroah-Hartman , Jiri Slaby , Ingo Molnar Cc: Muhammad Usama Anjum , kernel@collabora.com, stable@vger.kernel.org, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Subject: [PATCH v2 RESEND] tty/sysrq: replace smp_processor_id() with get_cpu() Date: Tue, 22 Aug 2023 14:01:11 +0500 Message-Id: <20230822090112.2601273-1-usama.anjum@collabora.com> X-Mailer: git-send-email 2.40.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The smp_processor_id() shouldn't be called from preemptible code. Instead use get_cpu() and put_cpu() which disables preemption in addition to getting the processor id. This fixes the following bug: [ 119.143590] sysrq: Show backtrace of all active CPUs [ 119.143902] BUG: using smp_processor_id() in preemptible [00000000] code= : bash/873 [ 119.144586] caller is debug_smp_processor_id+0x20/0x30 [ 119.144827] CPU: 6 PID: 873 Comm: bash Not tainted 5.10.124-dirty #3 [ 119.144861] Hardware name: QEMU QEMU Virtual Machine, BIOS 2023.05-1 07/= 22/2023 [ 119.145053] Call trace: [ 119.145093] dump_backtrace+0x0/0x1a0 [ 119.145122] show_stack+0x18/0x70 [ 119.145141] dump_stack+0xc4/0x11c [ 119.145159] check_preemption_disabled+0x100/0x110 [ 119.145175] debug_smp_processor_id+0x20/0x30 [ 119.145195] sysrq_handle_showallcpus+0x20/0xc0 [ 119.145211] __handle_sysrq+0x8c/0x1a0 [ 119.145227] write_sysrq_trigger+0x94/0x12c [ 119.145247] proc_reg_write+0xa8/0xe4 [ 119.145266] vfs_write+0xec/0x280 [ 119.145282] ksys_write+0x6c/0x100 [ 119.145298] __arm64_sys_write+0x20/0x30 [ 119.145315] el0_svc_common.constprop.0+0x78/0x1e4 [ 119.145332] do_el0_svc+0x24/0x8c [ 119.145348] el0_svc+0x10/0x20 [ 119.145364] el0_sync_handler+0x134/0x140 [ 119.145381] el0_sync+0x180/0x1c0 Cc: stable@vger.kernel.org Fixes: 47cab6a722d4 ("debug lockups: Improve lockup detection, fix generic = arch fallback") Signed-off-by: Muhammad Usama Anjum --- Changes since v1: - Add "Cc: stable@vger.kernel.org" tag --- drivers/tty/sysrq.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 23198e3f1461a..6b4a28bcf2f5f 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -262,13 +262,14 @@ static void sysrq_handle_showallcpus(u8 key) if (in_hardirq()) regs =3D get_irq_regs(); =20 - pr_info("CPU%d:\n", smp_processor_id()); + pr_info("CPU%d:\n", get_cpu()); if (regs) show_regs(regs); else show_stack(NULL, NULL, KERN_INFO); =20 schedule_work(&sysrq_showallcpus); + put_cpu(); } } =20 --=20 2.40.1