From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A27BBC433DF for ; Wed, 3 Jun 2020 07:23:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7731520679 for ; Wed, 3 Jun 2020 07:23:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="DDKk6u1f" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726229AbgFCHXC (ORCPT ); Wed, 3 Jun 2020 03:23:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46438 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726024AbgFCHXB (ORCPT ); Wed, 3 Jun 2020 03:23:01 -0400 Received: from mail-pf1-x443.google.com (mail-pf1-x443.google.com [IPv6:2607:f8b0:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D5EA3C05BD43 for ; Wed, 3 Jun 2020 00:22:59 -0700 (PDT) Received: by mail-pf1-x443.google.com with SMTP id f3so1007970pfd.11 for ; Wed, 03 Jun 2020 00:22:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=jZZiPsh1/1zA6921CY7D2bWjWgixKjYO5KIMajFrFQ8=; b=DDKk6u1fPNb/T0ZtwX3dMrmOO5bXn9bW/74ghMD/pXRmyCkw7jHbkdxMetszKJfWtK veXD6gwYd4eg1cWIEvLDloPzbUZaYGBSDa+Re77ULD/sE8UNM1yQnk5bSSUyDMwpVy0T Y7/j995qyxR8dwC/OLtn2FZ/EM4qAtf/zb/7k5oZco0ZQ9nkQ7WZKn7LYnnaj6Pb7F+0 M+ufUnZY6LcZTwV9NRv33/1uMEfH8VN+TfqVcRO9atsUTTAg8vCmPmZx5ULTBcffYe/w 8UTxAfx3zUaZYcK2HxYcqge/Iahepaoo71EcX3albVDPYSOZDayyVb0cDQJgK8dhIluc M8Bw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=jZZiPsh1/1zA6921CY7D2bWjWgixKjYO5KIMajFrFQ8=; b=QVq1a/uhtTt/adULMKZfFRYgX9ZFGKLrgBhWraXmbtHDdOYNaOlyZRH2osp64MRNhk WXS8wIlNNdPLZ02MyB8TFOqHDamdxxPiHHAdPuXcRsehznYtWzxBpwx63L1a1qClsPQ7 Vs0OJUNxAJhsqfiSZx1b9bnZYIT0x7lQFJppnb7aarUAe4qN5Nsn32IFrFPrpXXev2Oj Y0XMDdg1GHJq/BdFGva0z/yhIul+hE7i4xQlpPtfz6g8mj4Qh2hiHUz6QM9ldRPs/lQJ F7sX2lpaFNl+MOWpbAwPR/gLe6oWt026zNDH1gbXrBaK88prl1ZVB53WOVNdZzFcF/KI 1rMg== X-Gm-Message-State: AOAM531V68fetH+EkIXlfJijCjR3L7K561w4g0uhUSWqGPtSPrKaV9iw i5P8fkk6b19/a+N5kcsRVkxDKg== X-Google-Smtp-Source: ABdhPJxe75iTddF1frjRbkTFjkRx0tyZwI/mCeAnINWyuHqzShSQl2ELt84iMQB4pkOjXgqZEA/mqw== X-Received: by 2002:a05:6a00:14d4:: with SMTP id w20mr15187904pfu.279.1591168979274; Wed, 03 Jun 2020 00:22:59 -0700 (PDT) Received: from localhost.localdomain ([117.252.66.248]) by smtp.gmail.com with ESMTPSA id j17sm1407272pjy.22.2020.06.03.00.22.53 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 03 Jun 2020 00:22:58 -0700 (PDT) From: Sumit Garg To: daniel.thompson@linaro.org Cc: kgdb-bugreport@lists.sourceforge.net, jason.wessel@windriver.com, dianders@chromium.org, pmladek@suse.com, sergey.senozhatsky@gmail.com, gregkh@linuxfoundation.org, jslaby@suse.com, linux-kernel@vger.kernel.org, Sumit Garg Subject: [PATCH v5 4/4] kdb: Switch to use safer dbg_io_ops over console APIs Date: Wed, 3 Jun 2020 12:52:15 +0530 Message-Id: <1591168935-6382-5-git-send-email-sumit.garg@linaro.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1591168935-6382-1-git-send-email-sumit.garg@linaro.org> References: <1591168935-6382-1-git-send-email-sumit.garg@linaro.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In kgdb context, calling console handlers aren't safe due to locks used in those handlers which could in turn lead to a deadlock. Although, using oops_in_progress increases the chance to bypass locks in most console handlers but it might not be sufficient enough in case a console uses more locks (VT/TTY is good example). Currently when a driver provides both polling I/O and a console then kdb will output using the console. We can increase robustness by using the currently active polling I/O driver (which should be lockless) instead of the corresponding console. For several common cases (e.g. an embedded system with a single serial port that is used both for console output and debugger I/O) this will result in no console handler being used. In order to achieve this we need to reverse the order of preference to use dbg_io_ops (uses polling I/O mode) over console APIs. So we just store "struct console" that represents debugger I/O in dbg_io_ops and while emitting kdb messages, skip console that matches dbg_io_ops console in order to avoid duplicate messages. After this change, "is_console" param becomes redundant and hence removed. Suggested-by: Daniel Thompson Signed-off-by: Sumit Garg Reviewed-by: Douglas Anderson --- drivers/tty/serial/kgdb_nmi.c | 2 +- drivers/tty/serial/kgdboc.c | 6 +++--- drivers/usb/early/ehci-dbgp.c | 3 ++- include/linux/kgdb.h | 5 ++--- kernel/debug/kdb/kdb_io.c | 4 +++- 5 files changed, 11 insertions(+), 9 deletions(-) diff --git a/drivers/tty/serial/kgdb_nmi.c b/drivers/tty/serial/kgdb_nmi.c index 5022447..6004c0c 100644 --- a/drivers/tty/serial/kgdb_nmi.c +++ b/drivers/tty/serial/kgdb_nmi.c @@ -50,7 +50,7 @@ static int kgdb_nmi_console_setup(struct console *co, char *options) * I/O utilities that messages sent to the console will automatically * be displayed on the dbg_io. */ - dbg_io_ops->is_console = true; + dbg_io_ops->cons = co; return 0; } diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c index 4139698..6e182aa 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -178,7 +178,7 @@ static int configure_kgdboc(void) goto noconfig; } - kgdboc_io_ops.is_console = 0; + kgdboc_io_ops.cons = NULL; kgdb_tty_driver = NULL; kgdboc_use_kms = 0; @@ -198,7 +198,7 @@ static int configure_kgdboc(void) int idx; if (cons->device && cons->device(cons, &idx) == p && idx == tty_line) { - kgdboc_io_ops.is_console = 1; + kgdboc_io_ops.cons = cons; break; } } @@ -511,7 +511,6 @@ static struct kgdb_io kgdboc_earlycon_io_ops = { .write_char = kgdboc_earlycon_put_char, .pre_exception = kgdboc_earlycon_pre_exp_handler, .deinit = kgdboc_earlycon_deinit, - .is_console = true, }; #define MAX_CONSOLE_NAME_LEN (sizeof((struct console *) 0)->name) @@ -558,6 +557,7 @@ static int __init kgdboc_earlycon_init(char *opt) } earlycon = con; + kgdboc_earlycon_io_ops.cons = con; pr_info("Going to register kgdb with earlycon '%s'\n", con->name); if (kgdb_register_io_module(&kgdboc_earlycon_io_ops) != 0) { earlycon = NULL; diff --git a/drivers/usb/early/ehci-dbgp.c b/drivers/usb/early/ehci-dbgp.c index ea0d531..775cf70 100644 --- a/drivers/usb/early/ehci-dbgp.c +++ b/drivers/usb/early/ehci-dbgp.c @@ -1058,7 +1058,8 @@ static int __init kgdbdbgp_parse_config(char *str) kgdbdbgp_wait_time = simple_strtoul(ptr, &ptr, 10); } kgdb_register_io_module(&kgdbdbgp_io_ops); - kgdbdbgp_io_ops.is_console = early_dbgp_console.index != -1; + if (early_dbgp_console.index != -1) + kgdbdbgp_io_ops.cons = &early_dbgp_console; return 0; } diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h index c62d764..529116b 100644 --- a/include/linux/kgdb.h +++ b/include/linux/kgdb.h @@ -276,8 +276,7 @@ struct kgdb_arch { * the I/O driver. * @post_exception: Pointer to a function that will do any cleanup work * for the I/O driver. - * @is_console: 1 if the end device is a console 0 if the I/O device is - * not a console + * @cons: valid if the I/O device is a console; else NULL. */ struct kgdb_io { const char *name; @@ -288,7 +287,7 @@ struct kgdb_io { void (*deinit) (void); void (*pre_exception) (void); void (*post_exception) (void); - int is_console; + struct console *cons; }; extern const struct kgdb_arch arch_kgdb_ops; diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c index 0e4f2ed..683a799 100644 --- a/kernel/debug/kdb/kdb_io.c +++ b/kernel/debug/kdb/kdb_io.c @@ -549,7 +549,7 @@ static void kdb_msg_write(const char *msg, int msg_len) if (msg_len == 0) return; - if (dbg_io_ops && !dbg_io_ops->is_console) { + if (dbg_io_ops) { const char *cp = msg; int len = msg_len; @@ -562,6 +562,8 @@ static void kdb_msg_write(const char *msg, int msg_len) for_each_console(c) { if (!(c->flags & CON_ENABLED)) continue; + if (c == dbg_io_ops->cons) + continue; /* * Set oops_in_progress to encourage the console drivers to * disregard their internal spin locks: in the current calling -- 2.7.4