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 D32FBC433E0 for ; Thu, 4 Jun 2020 10:02:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AE230206DC for ; Thu, 4 Jun 2020 10:02:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="SYdCbuGB" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728445AbgFDKB7 (ORCPT ); Thu, 4 Jun 2020 06:01:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40202 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726411AbgFDKB6 (ORCPT ); Thu, 4 Jun 2020 06:01:58 -0400 Received: from mail-pl1-x641.google.com (mail-pl1-x641.google.com [IPv6:2607:f8b0:4864:20::641]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 10031C03E96D for ; Thu, 4 Jun 2020 03:01:58 -0700 (PDT) Received: by mail-pl1-x641.google.com with SMTP id x11so2001780plv.9 for ; Thu, 04 Jun 2020 03:01:58 -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=SWaxGGeqdBIuWfi0Pr0m5m/UNqCqE+K7xfquz67qpwE=; b=SYdCbuGB3J+72xEODNYeEFFubJezd+u5T6ELue2n2bkROzHd2EyydUBLmsE7tEE5IK mDLRPEOakhiDKP/h8VqX7TsibzreU/6CF7HFgmH+zXZYwaPCR54DUJeiy3fMy1YG63UI rK28OvFotjU0s+B/3q9D7X//OQHu9ZAdFKMWgqVQfJqOoLU9LaFNApnfxsG4YaaWD24c rhJ2VbxifJv8HJF7kgkmixaChgR5AlHXdX4A0vElchU932cv+DatjB3YJlfb4cr3+sGY 1rlm7px04nPTYsYXd37BHB7bKDgqF+DSNLynDT1Mmv70C6Tx+Y+jsUTwO4DmNQ9e7RY4 bMLg== 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=SWaxGGeqdBIuWfi0Pr0m5m/UNqCqE+K7xfquz67qpwE=; b=hIB6DkqMuJK16np7N9/T/02TMIzgrQssQvP62oSUwIT3qIZpTg8SCCbi0Izikk1dnG 6o7Ig8lX9bbfD1KzDoNpv+b8kH5t0vYbMxmXN5B0/PyUg+BeOa39RS2JHIhn5Ay4URwi PfiHSJxSfSBiXIotGt3hLrDps+flFgq8NhcNV6BP1tbB3E0I1I3uLNUHV+yscYPYD6xU k4/CsWW/4t+uucDUJDnR1aLEDX2gnRjN60GOhuf5f+LWvJFeaG+tw+VR4F1WyWbZaF2S nT37WM5mhtQO3mZwI8Aob2KE5mOlX0p01DYx4T8ajITT1Ze3SRONFsQEqL05vIzsvMP5 ucTA== X-Gm-Message-State: AOAM530mpbcHxTvcYJx4WQyWnJYwKBkLf5crmIHLElgwQRdR5PXCixfT c3vu5wcesT6DXEPYT3xVlNb4hA== X-Google-Smtp-Source: ABdhPJw0mqKUcRmUd840WqEdRfBHzQiTtI08e9dRTAOEKoLenr0WoeMdzZUbKKaoxlDGWF8PFm/7LQ== X-Received: by 2002:a17:90a:aa8f:: with SMTP id l15mr5379447pjq.211.1591264917610; Thu, 04 Jun 2020 03:01:57 -0700 (PDT) Received: from localhost.localdomain ([117.252.66.248]) by smtp.gmail.com with ESMTPSA id np5sm5786992pjb.43.2020.06.04.03.01.52 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 04 Jun 2020 03:01:56 -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 v6 3/4] kdb: Make kdb_printf() console handling more robust Date: Thu, 4 Jun 2020 15:31:18 +0530 Message-Id: <1591264879-25920-4-git-send-email-sumit.garg@linaro.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1591264879-25920-1-git-send-email-sumit.garg@linaro.org> References: <1591264879-25920-1-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 While rounding up CPUs via NMIs, its possible that a rounded up CPU maybe holding a console port lock leading to kgdb master CPU stuck in a deadlock during invocation of console write operations. A similar deadlock could also be possible while using synchronous breakpoints. So in order to avoid such a deadlock, set oops_in_progress to encourage the console drivers to disregard their internal spin locks: in the current calling context the risk of deadlock is a bigger problem than risks due to re-entering the console driver. We operate directly on oops_in_progress rather than using bust_spinlocks() because the calls bust_spinlocks() makes on exit are not appropriate for this calling context. Suggested-by: Sergey Senozhatsky Signed-off-by: Sumit Garg Reviewed-by: Douglas Anderson Revieved-by: Petr Mladek --- kernel/debug/kdb/kdb_io.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c index 58b7d25..0e4f2ed 100644 --- a/kernel/debug/kdb/kdb_io.c +++ b/kernel/debug/kdb/kdb_io.c @@ -562,7 +562,18 @@ static void kdb_msg_write(const char *msg, int msg_len) for_each_console(c) { if (!(c->flags & CON_ENABLED)) continue; + /* + * Set oops_in_progress to encourage the console drivers to + * disregard their internal spin locks: in the current calling + * context the risk of deadlock is a bigger problem than risks + * due to re-entering the console driver. We operate directly on + * oops_in_progress rather than using bust_spinlocks() because + * the calls bust_spinlocks() makes on exit are not appropriate + * for this calling context. + */ + ++oops_in_progress; c->write(c, msg, msg_len); + --oops_in_progress; touch_nmi_watchdog(); } } -- 2.7.4