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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 CDAABC5CFC0 for ; Mon, 18 Jun 2018 06:37:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7D73E20874 for ; Mon, 18 Jun 2018 06:37:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="NjxlU2GY" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7D73E20874 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754948AbeFRGhp (ORCPT ); Mon, 18 Jun 2018 02:37:45 -0400 Received: from mail-pl0-f67.google.com ([209.85.160.67]:43632 "EHLO mail-pl0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754488AbeFRGhn (ORCPT ); Mon, 18 Jun 2018 02:37:43 -0400 Received: by mail-pl0-f67.google.com with SMTP id c41-v6so8458458plj.10; Sun, 17 Jun 2018 23:37:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=UU9wh6H1HxCu4gGng/TPG2e9TfsdTYFS9ti4DmNN3KY=; b=NjxlU2GY37Hgz2p54syrKrj7CGlWCZyCt6KnPI6VFVoks83ufsmqgPoH5bXXSVsZ7o tNt8R0CAyaueiPsKuXdg49qxSysFoY0vm9ay87XqmfMEoPjIrEOmVqtvju09DShtMgM+ lXqBQqeXePbyverY4R19/yWFICvn7xGkFKjJNJtOvI5B9SgiZQ0CJaSNXT1MG4wLl1jf j7mVqRbcuByvzmcoK8jti5SPO+l43jJCOChfNjmd7ZP/diOYThbUadQYKw+E8uAPRlNp yavq44s5zvYgdF5B/9d9t+4QQ67ox1U8DHV+B0kcIO2E1uTYa3MT0AZF4aVufFzs+RL0 2NTQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=UU9wh6H1HxCu4gGng/TPG2e9TfsdTYFS9ti4DmNN3KY=; b=BEWpHr030VbuPh/g1dknOvqGrpEgMiQmdzz/OhMsqMBafcMHU4djCfr0wqTGcJGPAE 5elanqwGs/3AP66/R+WeQeeiqu+9p1tTLu8F5yFpsY2xpIj+9ws1A15+aTO3P4FvR2/w 5KY9eoxOQtQY9zxWeP/GaqHFbAJisSjqU7hM29H3Zy77yIDXGcBjLzm5an3QPjit1Rxv LLL0Q9lP76cpUuLrHZQeIRr9CvGyTJtt18pj9HVMamA0VKCzo+HAEX5p7lBJKFyba3QB XRAoCyVqmQOAH8bCwjkKXTtOlb4l7zKquWpOVAY+mnCv5iZjkoEiV4Sgwkox1R2LaThh LdGA== X-Gm-Message-State: APt69E2j2bs9zT3F7chUxBqTmfiLdJhmI2XEL4OzLl6h6VPOKsZvT+Yg rS2qn+hpsxrk8FUxu+aGOm4= X-Google-Smtp-Source: ADUXVKJ+KIpmqbHt6OIZqVbZDfyyNpt3BO9DILLOSRllcH6FzCXAXYYfvPSKZ1p3rvBnMMOhP6GVDw== X-Received: by 2002:a17:902:6e01:: with SMTP id u1-v6mr12585766plk.96.1529303863116; Sun, 17 Jun 2018 23:37:43 -0700 (PDT) Received: from localhost ([110.70.54.122]) by smtp.gmail.com with ESMTPSA id q9-v6sm16733795pgv.84.2018.06.17.23.37.40 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 17 Jun 2018 23:37:41 -0700 (PDT) Date: Mon, 18 Jun 2018 15:37:38 +0900 From: Sergey Senozhatsky To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Peter Zijlstra , Tetsuo Handa , Sergey Senozhatsky , linux-kernel@vger.kernel.org, "4 . 13+" Subject: Re: [PATCH] printk/nmi: Prevent deadlock when serializing NMI backtraces Message-ID: <20180618063738.GC27996@jagdpanzerIV> References: <20180517143903.19339-1-pmladek@suse.com> <20180605124729.3vix5nlkjpjzdljx@pathway.suse.cz> <20180606051029.GA19211@tigerII.localdomain> <20180606103356.GB19211@tigerII.localdomain> <20180608104825.e7xoxteelaxnwx66@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180608104825.e7xoxteelaxnwx66@pathway.suse.cz> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (06/08/18 12:48), Petr Mladek wrote: [..] > diff --git a/include/linux/printk.h b/include/linux/printk.h > index 6d7e800affd8..872fbdf8df26 100644 > --- a/include/linux/printk.h > +++ b/include/linux/printk.h > @@ -148,9 +148,13 @@ void early_printk(const char *s, ...) { } > #ifdef CONFIG_PRINTK_NMI > extern void printk_nmi_enter(void); > extern void printk_nmi_exit(void); > +extern void printk_nmi_direct_enter(void); > +extern void printk_nmi_direct_exit(void); > #else > static inline void printk_nmi_enter(void) { } > static inline void printk_nmi_exit(void) { } > +static void printk_nmi_direct_enter(void) { } > +static void printk_nmi_direct_exit(void) { } Can we have better names may be? Since direct printk_nmi is not in fact always `direct'. > +#ifdef CONFIG_PRINTK_NMI > +__printf(1, 0) int vprintk_nmi(const char *fmt, va_list args); > +#else > +__printf(1, 0) int vprintk_nmi(const char *fmt, va_list args) { return 0; } > +#endif Hmm, printk_safe.c knows about printk.c, printk.c knows about printk_safe.c. > __printf(1, 0) int vprintk_default(const char *fmt, va_list args); > __printf(1, 0) int vprintk_deferred(const char *fmt, va_list args); > __printf(1, 0) int vprintk_func(const char *fmt, va_list args); > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 247808333ba4..cf55bece43d9 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -1845,7 +1845,13 @@ asmlinkage int vprintk_emit(int facility, int level, > printk_delay(); > > /* This stops the holder of console_sem just where we want him */ > - logbuf_lock_irqsave(flags); > + printk_safe_enter_irqsave(flags); > + if (in_nmi() && !raw_spin_trylock(&logbuf_lock)) { > + printed_len = vprintk_nmi(fmt, args); > + printk_safe_exit_irqrestore(flags); > + return printed_len; > + } else > + raw_spin_lock(&logbuf_lock); OK... Can we do this in vprintk_func()? The race window should be super tiny [if matters at all], but in exchange we don't have to mix nmi, printk, printk_mni, etc. So over all I understand why you did it this way. May be I'd prefer to have less universal but shorter solution (e.g. modify only nmi_backtrace function and put there "printk_nmi_restricted_buffer"), but I won't really object your patch [unless I see some real issues with it]. -ss