From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: Re: [PATCH 00/50] Add log level to show_stack() Date: Wed, 13 Nov 2019 10:44:46 -0500 Message-ID: <20191113104446.419e4d8a@gandalf.local.home> References: <20191106030542.868541-1-dima@arista.com> <20191106092039.GT4131@hirez.programming.kicks-ass.net> <10db6fa1-5b17-ebe6-09e0-6335e09e4db8@arista.com> <20191106203440.GH3079@worktop.programming.kicks-ass.net> <20191106232512.GU25745@shell.armlinux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=1FcMnrlSz7GnnA3DU9kLB2rkj6wtu0Uh/x/5dLvxumw=; b=kVY5OSbjNxqndK bDsErsGS8qOEfMKGrHCX4mmwI5wYomt4bG5nRYvmi3bXg2F3KupiIvDQkSL6TtyJ9GqJWKLyDdht1 p2/vsepkB7HZuDMS5NFoU7t1M2yf1HHeMJaTx9RIhxSTM6p1jncEbSach3EsH45Wqk1GRWQ2xumQ7 qYLvMS9Iy+XfOOlR/qaLk1nb8G8hNN3OLXSxgCwMbXVK9xnywqSVI9aMCFEASpXpzyIPE0fnrCtla ZgMny4bmYNYPg9CdOqO3Le+IQ6Nf5BX9HGiOr5tpXLZ9t5drTwIm8s2R3fdCksOdao67DkDl6TmKM 76GetKgassVu8sezUuGw==; In-Reply-To: <20191106232512.GU25745@shell.armlinux.org.uk> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+glpr-linux-riscv=m.gmane.org@lists.infradead.org To: Russell King - ARM Linux admin Cc: Juri Lelli , linux-sh@vger.kernel.org, Catalin Marinas , Ben Segall , Guo Ren , Pavel Machek , Vincent Guittot , Paul Burton , Dmitry Safonov , Michael Ellerman , Geert Uytterhoeven , Mel Gorman , Jiri Slaby , Matt Turner , uclinux-h8-devel@lists.sourceforge.jp, Len Brown , linux-pm@vger.kernel.org, Heiko Carstens , linux-um@lists.infradead.org, Thomas Gleixner , Dietmar Eggemann , Richard Henderson , Greg Kroah-Hartman , "Rafael J. Wysocki" , linux-kerne On Wed, 6 Nov 2019 23:25:13 +0000 Russell King - ARM Linux admin wrote: > On Wed, Nov 06, 2019 at 09:34:40PM +0100, Peter Zijlstra wrote: > > I suppose I'm surprised there are backtraces that are not important. > > Either badness happened and it needs printing, or the user asked for it > > and it needs printing. > > Or utterly meaningless. > > > Perhaps we should be removing backtraces if they're not important > > instead of allowing to print them as lower loglevels? > > Definitely! WARN_ON() is well overused - and as is typical, used > without much thought. Bound to happen after Linus got shirty about > BUG_ON() being over used. Everyone just grabbed the next nearest thing > to assert(). > > As a kind of example, I've recently come across one WARN_ON() in a > driver subsystem (that shall remain nameless at the moment) which very > likely has multiple different devices on a platform. The WARN_ON() > triggers as a result of a problem with the hardware, but because it's a > WARN_ON(), you've no idea which device has a problem. The backtrace is > mostly meaningless. So you know that a problem has occurred, but the > kernel prints *useless* backtrace to let you know, and totally omits > the *useful* information. > I would like to bring up a topic for the next maintainers summit (although I may not even be there), that we define a clear use of WARN_ON(). I use it only if the code does something I do not expect it to do, and is considered a bug in the code if it triggers. But it appears that some drivers use it for "oh I didn't realize this hardware does something I didn't expect". And is ignored when the warn on is triggered and reported, with "you have buggy hardware" but my hardware appears to work just fine! -- Steve