From patchwork Fri Aug 19 22:17:31 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Guilherme G. Piccoli" X-Patchwork-Id: 12949319 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 620A9C32789 for ; Fri, 19 Aug 2022 22:27:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242222AbiHSW1I (ORCPT ); Fri, 19 Aug 2022 18:27:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54148 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242215AbiHSW1G (ORCPT ); Fri, 19 Aug 2022 18:27:06 -0400 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 26700112331; Fri, 19 Aug 2022 15:27:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Sender:Reply-To:Content-Type:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=bwBb3Wqkav6yGYTcSOKgHtTuFq6y9W8T2JmU+7U+WFw=; b=FPIhhlYmbA7Ekd0SbUE79tFQuq sD7VF0K26UYnuYDL/GpMEqpIndV32PKyaEf3+hLJtzhpUgMvejS6b08pKh0EDi1XNiocxGbRtpA5A dFRzLqe44KDmWV0NpqXAEy1n9hNo/BgL5WhLnaSSGLFMIhjwuIGgJ6Y8f+5KmTj3+M6XIeLsawto5 3LG9bcijhNeCZXf5dfWrlTxTUd8zrf3C8miCJGksaHHYASbw37n3YqclWfd35S5tONxjbfrzriRon GjsDoQlXa4+rQ3fkp03slSd7Di/jYXir/5aJghvsv9DM/e3vg/LUwdJt7Y35Nl7voPZEOsFUMntUi zWl13YyA==; Received: from [179.232.144.59] (helo=localhost) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1oPAS8-00CbFM-Vn; Sat, 20 Aug 2022 00:26:59 +0200 From: "Guilherme G. Piccoli" To: akpm@linux-foundation.org, bhe@redhat.com, pmladek@suse.com, kexec@lists.infradead.org Cc: linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, netdev@vger.kernel.org, x86@kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net, halves@canonical.com, fabiomirmar@gmail.com, alejandro.j.jimenez@oracle.com, andriy.shevchenko@linux.intel.com, arnd@arndb.de, bp@alien8.de, corbet@lwn.net, d.hatayama@jp.fujitsu.com, dave.hansen@linux.intel.com, dyoung@redhat.com, feng.tang@intel.com, gregkh@linuxfoundation.org, mikelley@microsoft.com, hidehiro.kawai.ez@hitachi.com, jgross@suse.com, john.ogness@linutronix.de, keescook@chromium.org, luto@kernel.org, mhiramat@kernel.org, mingo@redhat.com, paulmck@kernel.org, peterz@infradead.org, rostedt@goodmis.org, senozhatsky@chromium.org, stern@rowland.harvard.edu, tglx@linutronix.de, vgoyal@redhat.com, vkuznets@redhat.com, will@kernel.org, xuqiang36@huawei.com, "Guilherme G. Piccoli" Subject: [PATCH V3 11/11] panic: Fixes the panic_print NMI backtrace setting Date: Fri, 19 Aug 2022 19:17:31 -0300 Message-Id: <20220819221731.480795-12-gpiccoli@igalia.com> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220819221731.480795-1-gpiccoli@igalia.com> References: <20220819221731.480795-1-gpiccoli@igalia.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Commit 8d470a45d1a6 ("panic: add option to dump all CPUs backtraces in panic_print") introduced a setting for the "panic_print" kernel parameter to allow users to request a NMI backtrace on panic. Problem is that the panic_print handling happens after the secondary CPUs are already disabled, hence this option ended-up being kind of a no-op - kernel skips the NMI trace in idling CPUs, which is the case of offline CPUs. Fix it by checking the NMI backtrace bit in the panic_print prior to the CPU disabling function. Fixes: 8d470a45d1a6 ("panic: add option to dump all CPUs backtraces in panic_print") Cc: Feng Tang Cc: Petr Mladek Signed-off-by: Guilherme G. Piccoli --- V3: - No changes. V2: - new patch, there was no V1 of this one. Hi folks, thanks upfront for reviews. This is a new patch, fixing an issue I found in my tests, so I shoved it into this fixes series. Notice that while at it, I got rid of the "crash_kexec_post_notifiers" local copy in panic(). This was introduced by commit b26e27ddfd2a ("kexec: use core_param for crash_kexec_post_notifiers boot option"), but it is not clear from comments or commit message why this local copy is required. My understanding is that it's a mechanism to prevent some concurrency, in case some other CPU modify this variable while panic() is running. I find it very unlikely, hence I removed it - but if people consider this copy needed, I can respin this patch and keep it, even providing a comment about that, in order to be explict about its need. Let me know your thoughts! Cheers, Guilherme kernel/panic.c | 47 +++++++++++++++++++++++++++-------------------- 1 file changed, 27 insertions(+), 20 deletions(-) diff --git a/kernel/panic.c b/kernel/panic.c index c6eb8f8db0c0..b025a8f21c17 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -180,9 +180,6 @@ static void panic_print_sys_info(bool console_flush) return; } - if (panic_print & PANIC_PRINT_ALL_CPU_BT) - trigger_all_cpu_backtrace(); - if (panic_print & PANIC_PRINT_TASK_INFO) show_state(); @@ -199,6 +196,30 @@ static void panic_print_sys_info(bool console_flush) ftrace_dump(DUMP_ALL); } +/* + * Helper that triggers the NMI backtrace (if set in panic_print) + * and then performs the secondary CPUs shutdown - we cannot have + * the NMI backtrace after the CPUs are off! + */ +static void panic_other_cpus_shutdown(void) +{ + if (panic_print & PANIC_PRINT_ALL_CPU_BT) + trigger_all_cpu_backtrace(); + + /* + * Note that smp_send_stop() is the usual SMP shutdown function, + * which unfortunately may not be hardened to work in a panic + * situation. If we want to do crash dump after notifier calls + * and kmsg_dump, we will need architecture dependent extra + * bits in addition to stopping other CPUs, hence we rely on + * crash_smp_send_stop() for that. + */ + if (!crash_kexec_post_notifiers) + smp_send_stop(); + else + crash_smp_send_stop(); +} + /** * panic - halt the system * @fmt: The text string to print @@ -214,7 +235,6 @@ void panic(const char *fmt, ...) long i, i_next = 0, len; int state = 0; int old_cpu, this_cpu; - bool _crash_kexec_post_notifiers = crash_kexec_post_notifiers; if (panic_on_warn) { /* @@ -289,23 +309,10 @@ void panic(const char *fmt, ...) * * Bypass the panic_cpu check and call __crash_kexec directly. */ - if (!_crash_kexec_post_notifiers) { + if (!crash_kexec_post_notifiers) __crash_kexec(NULL); - /* - * Note smp_send_stop is the usual smp shutdown function, which - * unfortunately means it may not be hardened to work in a - * panic situation. - */ - smp_send_stop(); - } else { - /* - * If we want to do crash dump after notifier calls and - * kmsg_dump, we will need architecture dependent extra - * works in addition to stopping other CPUs. - */ - crash_smp_send_stop(); - } + panic_other_cpus_shutdown(); /* * Run any panic handlers, including those that might need to @@ -326,7 +333,7 @@ void panic(const char *fmt, ...) * * Bypass the panic_cpu check and call __crash_kexec directly. */ - if (_crash_kexec_post_notifiers) + if (crash_kexec_post_notifiers) __crash_kexec(NULL); #ifdef CONFIG_VT