From patchwork Mon Oct 9 16:20:20 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Muhammad Usama Anjum X-Patchwork-Id: 731837 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 309D5CD6102 for ; Mon, 9 Oct 2023 16:20:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346628AbjJIQUm (ORCPT ); Mon, 9 Oct 2023 12:20:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39640 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346619AbjJIQUl (ORCPT ); Mon, 9 Oct 2023 12:20:41 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6BBE6A6; Mon, 9 Oct 2023 09:20:37 -0700 (PDT) Received: from localhost.localdomain (unknown [116.71.10.238]) (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 028206607038; Mon, 9 Oct 2023 17:20:32 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1696868436; bh=KAhhKO4g/GCRCekMIhf+cXHcdkyda+W3DvR4reXU71Q=; h=From:To:Cc:Subject:Date:From; b=a0xU1lr7jX1hDVGJIPpbK+z/xLeaBa5BctJgH0/H9L9DDq3NqBjL2VPpkeUu1QTdj JXUOdxSX4SsLLYZaO1ggNwlUOGkVIrHjLk924CjzPhqhEyXM0JE/cvlWFi/FDqbPOR 3OePQjYqNv1wOTrw/tJ3rjFqKqQXR6y6qL+KJqvzL/Z1AeuKOsZyBvtNoHgcJf8G0i n7Wsb/tpkvCxaaFaSWQdyBO7EAB+Xccws80sKknJyI4ZX4x/Zaf5BK8oa3nZvLT0yd HMUeepbvH9gOi9/BCrdOmO/bFAaF/h6Uq154ezlE7XfnL34HoEWVjOk6SBb50VjpyT U36WuxfVjevWg== 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 v4] tty/sysrq: replace smp_processor_id() with get_cpu() Date: Mon, 9 Oct 2023 21:20:20 +0500 Message-Id: <20231009162021.3607632-1-usama.anjum@collabora.com> X-Mailer: git-send-email 2.40.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org 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. Enable preemption back after calling schedule_work() to make sure that the work gets scheduled on all cores other than the current core. We want to avoid a scenario where current core's stack trace is printed multiple times and one core's stack trace isn't printed because of scheduling of current task. 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: jirislaby@kernel.org Cc: stable@vger.kernel.org Fixes: 47cab6a722d4 ("debug lockups: Improve lockup detection, fix generic arch fallback") Signed-off-by: Muhammad Usama Anjum --- Changes since v3: - Update commit message to explain why preemption reenabling must happen after calling schedule_work() Changes since v2: - Add changelog and resend 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 = get_irq_regs(); - 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); schedule_work(&sysrq_showallcpus); + put_cpu(); } }