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,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 81698C433DF for ; Fri, 29 May 2020 11:27:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5517D207BC for ; Fri, 29 May 2020 11:27:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="aZK2+XXM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726836AbgE2L1o (ORCPT ); Fri, 29 May 2020 07:27:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40440 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725306AbgE2L1n (ORCPT ); Fri, 29 May 2020 07:27:43 -0400 Received: from mail-pg1-x541.google.com (mail-pg1-x541.google.com [IPv6:2607:f8b0:4864:20::541]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 351FCC03E969 for ; Fri, 29 May 2020 04:27:42 -0700 (PDT) Received: by mail-pg1-x541.google.com with SMTP id o6so546066pgh.2 for ; Fri, 29 May 2020 04:27:42 -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=mmVANo270ZVKU00Ntn1LhIr6gWxMXan2SJfCFjNoHEo=; b=aZK2+XXMoRhPCXVUxsDPkb9kSqkhrNLxdLS+VK2l0Him6ssCZoZ21SrepRXjgt/lH1 wPjs4bZldxfBqAaXCCEOgOuDzZIo90LTmU1RT/71D8xO0wPNCIUzGGSYGdQ/YlanXpD5 tymc4udXM1EAeCFRdG9SjmTIW5McowgBQ5xdltp87Mjr/9ZLzv6N3NqTBvAjgtCeoxsu v4PFPvGPqrYUCHiSh9M2l/R3XrNtZKY6OAI+2/ACo4+9Duzf3wYHSifzOX1jZu6qukFL /EKSR23Jf8Bwkh8PskSWU0NwhMmi3NCwCZz4IMTmvf/+sWcAWs4bWG8i+OfY2epqOy06 S+Zw== 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=mmVANo270ZVKU00Ntn1LhIr6gWxMXan2SJfCFjNoHEo=; b=sM/Xr4I7gOk3zUOJs+S+9k9vAUW+qsjF3zOFDeLU44YkqFAcdqDWr74SbI3b1G84hH d2+sCogT46F/Mk6AwnZlOkVY7gy2dfm9Fd7EN08vBSYEPaLr2k2XAeGSB/5SfkSiDAqY 2AVf/Efn5G9uuvYUB8jpnwqJ5WMEW2+/240sjE/kF5GmAaSM48Z9mtz3WQLEj2Dj76M6 yMad4cy3I3f4zEs800rHArKogkyGFp+UivxLJcmcJ3K0xAwu2Z0DuHdibSH8/bG+kIJA njkLB2LmGUFOKOfSx4ux4oIJNuUWQzptEkvDAXVKd2kwJDVfaIvUXL3TT/IEEQ6aBjOT 9yNw== X-Gm-Message-State: AOAM532o87hLwqcWAainSFv23PfOCE2+MZoo0WuyN2GXV66kV/17vxdu mgGocsWugrN24lY5FOTwDZJIsA== X-Google-Smtp-Source: ABdhPJzS/gqMxxiyYyZH1I3fTV851M9JRdWhE5v8GMU+1CdSJsblvJLl+ZsTF6SL8JmpR+LIeAWx2w== X-Received: by 2002:a62:2ad1:: with SMTP id q200mr8012952pfq.225.1590751661689; Fri, 29 May 2020 04:27:41 -0700 (PDT) Received: from localhost.localdomain ([117.252.66.248]) by smtp.gmail.com with ESMTPSA id w190sm7016741pfw.35.2020.05.29.04.27.36 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 29 May 2020 04:27:40 -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 v4 4/4] kdb: Switch to use safer dbg_io_ops over console APIs Date: Fri, 29 May 2020 16:56:47 +0530 Message-Id: <1590751607-29676-5-git-send-email-sumit.garg@linaro.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1590751607-29676-1-git-send-email-sumit.garg@linaro.org> References: <1590751607-29676-1-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 --- drivers/tty/serial/kgdb_nmi.c | 2 +- drivers/tty/serial/kgdboc.c | 4 ++-- drivers/usb/early/ehci-dbgp.c | 3 ++- include/linux/kgdb.h | 5 ++--- kernel/debug/kdb/kdb_io.c | 4 +++- 5 files changed, 10 insertions(+), 8 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 c9f94fa..c7ffa87 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -153,7 +153,7 @@ 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; @@ -173,7 +173,7 @@ 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; } } diff --git a/drivers/usb/early/ehci-dbgp.c b/drivers/usb/early/ehci-dbgp.c index ea0d531..8c32d1a 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 b072aeb..bc0face3 100644 --- a/include/linux/kgdb.h +++ b/include/linux/kgdb.h @@ -273,8 +273,7 @@ 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. */ struct kgdb_io { const char *name; @@ -284,7 +283,7 @@ struct kgdb_io { int (*init) (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 9e5a40d..5e00bc8 100644 --- a/kernel/debug/kdb/kdb_io.c +++ b/kernel/debug/kdb/kdb_io.c @@ -560,12 +560,14 @@ static void kdb_msg_write(char *msg, int msg_len) if (msg_len == 0) return; - if (dbg_io_ops && !dbg_io_ops->is_console) + if (dbg_io_ops) kdb_io_write(msg, 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