From patchwork Mon Feb 28 13:54:08 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sumit Garg X-Patchwork-Id: 546942 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 1F020C433F5 for ; Mon, 28 Feb 2022 13:54:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236233AbiB1NzA (ORCPT ); Mon, 28 Feb 2022 08:55:00 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45090 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236342AbiB1Ny6 (ORCPT ); Mon, 28 Feb 2022 08:54:58 -0500 Received: from mail-pl1-x630.google.com (mail-pl1-x630.google.com [IPv6:2607:f8b0:4864:20::630]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9C48C43498 for ; Mon, 28 Feb 2022 05:54:19 -0800 (PST) Received: by mail-pl1-x630.google.com with SMTP id u2so3213513ple.10 for ; Mon, 28 Feb 2022 05:54:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=WEy1zCQgDzZI0KWybQkh1tiSD7E5/9VujlwkP39Po4I=; b=S7MP84cNFACuxNfvhM7fJy4miwUvj6rX8/O5d5P3Tguai+qxHva7T8Sa+44kR26m4K rQg8xhy/dDkRLc8YoC0FocXWrtH+dOw2OKCYxNxZfQbib7HWrLHl+LCGckPX8KhY9RAL dznVnRIp37gF/yAOvrR3d9p0ZYjYxxUwX5i+jknC6gS10myUOCeukvn5ihIYJ3d/vKP7 6zGy3YLCOuTUN6OEIHGLTSI6kTk6ceOn2JpoabZcQph2qZjVG4s4ef2a4KnG9tvyoNHp 4A901AASZCniir/7Zb9MBw2Rah0hn8CFMhmF9N1cP/wLbl+y66SiFqJLA+QN+PWEXKre qQYA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=WEy1zCQgDzZI0KWybQkh1tiSD7E5/9VujlwkP39Po4I=; b=1EF9XG0q4b0Ijh27pdvHGeS8GH5uh2nZfS6juj4ocwwCcRfPHAExFMRuciDnZiIf0O //YDE6RMdS/fVfJofzSE4jz7qLIzw3smMNFsG4Var7TQxGlhHKzM6J1f88p/xOywO1F9 Bjj3b4dx99ZagQkGZFlF+QYi1lyIKIo/EBXjZ+DpJR4he8H8/Qz/174REDGb8+QzzUB2 f6obsB0rTLOZDL7xCGK+g434Xbaq6xdSa3hA+k1iMPsTZQaul/v0KziimkBqRrrajuPC +0erjYbrG8/vBE+JrktsGX3mTo3atBmycF24Cg+CtJl/u57NwgmubK96ATY3BkeNP++D KsEg== X-Gm-Message-State: AOAM530gw3acY5u5qw4cHtYy6Yt6inWlOIRgEcECs1uLN9QcdtuXZy2k 3Zv+Qqf2xyOoM0Y14WilPuWJbnv7IIfp7w== X-Google-Smtp-Source: ABdhPJxndjCL6DuOrGcZ40lddkjyZWeCgJNEwhO3fREhBQx7ptcnk3zS+oVQVdJ71WNlar0BPJv41A== X-Received: by 2002:a17:90a:fef:b0:1bc:1465:c4e9 with SMTP id 102-20020a17090a0fef00b001bc1465c4e9mr16919511pjz.119.1646056458698; Mon, 28 Feb 2022 05:54:18 -0800 (PST) Received: from localhost.localdomain ([2401:4900:1c2a:216d:26eb:507e:a508:58b5]) by smtp.gmail.com with ESMTPSA id q9-20020a056a00088900b004e03b051040sm13894746pfj.112.2022.02.28.05.54.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Feb 2022 05:54:18 -0800 (PST) From: Sumit Garg To: linux-serial@vger.kernel.org, hasegawa-hitomi@fujitsu.com Cc: gregkh@linuxfoundation.org, jirislaby@kernel.org, jason.wessel@windriver.com, daniel.thompson@linaro.org, dianders@chromium.org, linux-kernel@vger.kernel.org, kgdb-bugreport@lists.sourceforge.net, arnd@arndb.de, peterz@infradead.org, Sumit Garg Subject: [RFT v3] tty/sysrq: Make sysrq handler NMI aware Date: Mon, 28 Feb 2022 19:24:08 +0530 Message-Id: <20220228135408.1452882-1-sumit.garg@linaro.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Allow a magic sysrq to be triggered from an NMI context. This is done via marking some sysrq actions as NMI safe. Safe actions will be allowed to run from NMI context whilst that cannot run from an NMI will be queued as irq_work for later processing. The major use-case is to add NMI debugging capabilities to the kernel in order to debug scenarios such as: - Primary CPU is stuck in deadlock with interrupts disabled and hence doesn't honor serial device interrupt. So having magic sysrq triggered as an NMI is helpful for debugging. - Always enabled NMI based magic sysrq irrespective of whether the serial TTY port is active or not. - Apart from UART interrupts, it allows magic sysrq to be triggered from a diagnostic NMI interrupt on systems such as A64FX. A particular sysrq handler is only marked as NMI safe in case the handler isn't contending for any synchronization primitives as in NMI context they are expected to cause deadlocks. Note that the debug sysrq do not contend for any synchronization primitives. It does call kgdb_breakpoint() to provoke a trap but that trap handler should be NMI safe on architectures that implement an NMI. Signed-off-by: Sumit Garg --- Hi Hitomi Hasegawa, Give this patch a try with diagnostic pseudo NMI interrupt on A64FX and let me know if it works for you. Also, feel free to include this patch along with your driver patch. -Sumit Changes in v3: - Extend commit message to include use-cases. - Get rid of redundant kfifo stuff. - Incorporate other misc. feedback from Peter Z. Changes in v2: - Rebased to 5.17-rc5. - Separate this patch from complete patch-set [1] as its relevant for other diagnostic NMI interrupts [2] as well apart from uart NMI interrupts. - Incorporated suggestions from Doug. [1] https://lore.kernel.org/linux-arm-kernel/CAFA6WYOWHgmYYt=KGXDh2hKiuy_rQbJfi279ev0+s-Qh7L21kA@mail.gmail.com/t/#m2b5006f08581448020eb24566927a104d0b95c44 [2] https://lore.kernel.org/all/Yhi0rrkSR63ZhjX1@kroah.com/T/ drivers/tty/sysrq.c | 45 ++++++++++++++++++++++++++++++++++++++- include/linux/sysrq.h | 1 + kernel/debug/debug_core.c | 1 + 3 files changed, 46 insertions(+), 1 deletion(-) diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index bbfd004449b5..40cd492fe6ec 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -51,6 +51,7 @@ #include #include #include +#include #include #include @@ -112,6 +113,7 @@ static const struct sysrq_key_op sysrq_loglevel_op = { .help_msg = "loglevel(0-9)", .action_msg = "Changing Loglevel", .enable_mask = SYSRQ_ENABLE_LOG, + .nmi_safe = true, }; #ifdef CONFIG_VT @@ -159,6 +161,7 @@ static const struct sysrq_key_op sysrq_crash_op = { .help_msg = "crash(c)", .action_msg = "Trigger a crash", .enable_mask = SYSRQ_ENABLE_DUMP, + .nmi_safe = true, }; static void sysrq_handle_reboot(int key) @@ -172,6 +175,7 @@ static const struct sysrq_key_op sysrq_reboot_op = { .help_msg = "reboot(b)", .action_msg = "Resetting", .enable_mask = SYSRQ_ENABLE_BOOT, + .nmi_safe = true, }; const struct sysrq_key_op *__sysrq_reboot_op = &sysrq_reboot_op; @@ -219,6 +223,7 @@ static const struct sysrq_key_op sysrq_showlocks_op = { .handler = sysrq_handle_showlocks, .help_msg = "show-all-locks(d)", .action_msg = "Show Locks Held", + .nmi_safe = true, }; #else #define sysrq_showlocks_op (*(const struct sysrq_key_op *)NULL) @@ -291,6 +296,7 @@ static const struct sysrq_key_op sysrq_showregs_op = { .help_msg = "show-registers(p)", .action_msg = "Show Regs", .enable_mask = SYSRQ_ENABLE_DUMP, + .nmi_safe = true, }; static void sysrq_handle_showstate(int key) @@ -328,6 +334,7 @@ static const struct sysrq_key_op sysrq_ftrace_dump_op = { .help_msg = "dump-ftrace-buffer(z)", .action_msg = "Dump ftrace buffer", .enable_mask = SYSRQ_ENABLE_DUMP, + .nmi_safe = true, }; #else #define sysrq_ftrace_dump_op (*(const struct sysrq_key_op *)NULL) @@ -566,6 +573,32 @@ static void __sysrq_put_key_op(int key, const struct sysrq_key_op *op_p) sysrq_key_table[i] = op_p; } +static int sysrq_nmi_key = -1; + +static void sysrq_do_irq_work(struct irq_work *work) +{ + const struct sysrq_key_op *op_p; + int orig_suppress_printk; + + orig_suppress_printk = suppress_printk; + suppress_printk = 0; + + rcu_sysrq_start(); + rcu_read_lock(); + + op_p = __sysrq_get_key_op(sysrq_nmi_key); + if (op_p) + op_p->handler(sysrq_nmi_key); + + rcu_read_unlock(); + rcu_sysrq_end(); + + suppress_printk = orig_suppress_printk; + sysrq_nmi_key = -1; +} + +static DEFINE_IRQ_WORK(sysrq_irq_work, sysrq_do_irq_work); + void __handle_sysrq(int key, bool check_mask) { const struct sysrq_key_op *op_p; @@ -573,6 +606,10 @@ void __handle_sysrq(int key, bool check_mask) int orig_suppress_printk; int i; + /* Skip sysrq handling if one already in progress */ + if (sysrq_nmi_key != -1) + return; + orig_suppress_printk = suppress_printk; suppress_printk = 0; @@ -596,7 +633,13 @@ void __handle_sysrq(int key, bool check_mask) if (!check_mask || sysrq_on_mask(op_p->enable_mask)) { pr_info("%s\n", op_p->action_msg); console_loglevel = orig_log_level; - op_p->handler(key); + + if (in_nmi() && !op_p->nmi_safe) { + sysrq_nmi_key = key; + irq_work_queue(&sysrq_irq_work); + } else { + op_p->handler(key); + } } else { pr_info("This sysrq operation is disabled.\n"); console_loglevel = orig_log_level; diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h index 3a582ec7a2f1..630b5b9dc225 100644 --- a/include/linux/sysrq.h +++ b/include/linux/sysrq.h @@ -34,6 +34,7 @@ struct sysrq_key_op { const char * const help_msg; const char * const action_msg; const int enable_mask; + const bool nmi_safe; }; #ifdef CONFIG_MAGIC_SYSRQ diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c index da06a5553835..53b56114f59b 100644 --- a/kernel/debug/debug_core.c +++ b/kernel/debug/debug_core.c @@ -978,6 +978,7 @@ static const struct sysrq_key_op sysrq_dbg_op = { .handler = sysrq_handle_dbg, .help_msg = "debug(g)", .action_msg = "DEBUG", + .nmi_safe = true, }; #endif