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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 496B7C43603 for ; Mon, 1 Mar 2021 16:23:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 177ED64EEA for ; Mon, 1 Mar 2021 16:23:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237890AbhCAQXQ (ORCPT ); Mon, 1 Mar 2021 11:23:16 -0500 Received: from mx2.suse.de ([195.135.220.15]:48570 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237647AbhCAQRX (ORCPT ); Mon, 1 Mar 2021 11:17:23 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1614615395; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qjU6LlsD5TNSSL5FEBNOVxATeEEJK5IHJtgvq5ED2kQ=; b=Jt+XFXN0OOpDt75X4ddCJuqiJ15OWsbUD30Ikn40ppgVMzlyrWcUqYYHslDf0Qb0Ja2ija ji9un9tfz6jCgnNMuJR5xcN/bYl2OIlveP7rvP8NiooMwLe5yndizuhwszF2T8f6lVGYCd c2FvzBdzwMpRAWzUvIxQl5MAtKU4QPQ= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 88191AE05; Mon, 1 Mar 2021 16:16:35 +0000 (UTC) Date: Mon, 1 Mar 2021 17:16:34 +0100 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Jeff Dike , Richard Weinberger , Anton Ivanov , Thomas Meyer , Andy Shevchenko , linux-um@lists.infradead.org Subject: Re: [PATCH next v3 01/15] um: synchronize kmsg_dumper Message-ID: References: <20210225202438.28985-1-john.ogness@linutronix.de> <20210225202438.28985-2-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210225202438.28985-2-john.ogness@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2021-02-25 21:24:24, John Ogness wrote: > The kmsg_dumper can be called from any context and CPU, possibly > from multiple CPUs simultaneously. Since a static buffer is used > to retrieve the kernel logs, this buffer must be protected against > simultaneous dumping. Skip dumping if another context is already > dumping. > > Signed-off-by: John Ogness > Reviewed-by: Petr Mladek > --- > arch/um/kernel/kmsg_dump.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c > index 6516ef1f8274..4869e2cc787c 100644 > --- a/arch/um/kernel/kmsg_dump.c > +++ b/arch/um/kernel/kmsg_dump.c > @@ -1,5 +1,6 @@ > // SPDX-License-Identifier: GPL-2.0 > #include > +#include > #include > #include > #include > @@ -9,6 +10,7 @@ > static void kmsg_dumper_stdout(struct kmsg_dumper *dumper, > enum kmsg_dump_reason reason) > { > + static DEFINE_SPINLOCK(lock); > static char line[1024]; > struct console *con; > size_t len = 0; > @@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper, > if (con) > return; > > + if (!spin_trylock(&lock)) I have almost missed this. It is wrong. The last version correctly used if (!spin_trylock_irqsave(&lock, flags)) kmsg_dump(KMSG_DUMP_PANIC) is called in panic() with interrupts disabled. We have to store the flags here. Best Regards, Petr