From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hrndva-omtalb.mail.rr.com (hrndva-omtalb.mail.rr.com [71.74.56.122]) by ozlabs.org (Postfix) with ESMTP id D80A82C007A for ; Thu, 13 Jun 2013 22:45:09 +1000 (EST) Message-ID: <1371127506.9844.275.camel@gandalf.local.home> Subject: Re: [PATCH] powerpc: Fix stack overflow crash in resume_kernel when ftracing From: Steven Rostedt To: Michael Ellerman Date: Thu, 13 Jun 2013 08:45:06 -0400 In-Reply-To: <1371121496-16095-1-git-send-email-michael@ellerman.id.au> References: <1371121496-16095-1-git-send-email-michael@ellerman.id.au> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org, Anton Blanchard List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2013-06-13 at 21:04 +1000, Michael Ellerman wrote: > Although that should be sufficient to fix the bug, we also mark the > runlatch routines as notrace. They are called very early in the > exception entry and we are asking for trouble tracing them. They are > also fairly uninteresting and tracing them just adds unnecessary > overhead. Note, I usually lean towards tracing everything that can be traced, and only adding notrace to things that will actually cause a crash. If you don't like them to be traced, you can always do: echo '*__ppc64_runlatch_*' > /sys/kernel/debug/tracing/set_ftrace_notrace and that will keep them from being traced. You can also add it to the kernel command line with: ftrace_notrace=*__ppc64_runlatch_* which will also disable them on boot up. Also trace-cmd has: trace-cmd record -p function_graph -n '*__ppc64_runlatch_*' that will do the same thing. Hmm, I should add a way to disable things that are usually considered noise. Perhaps add something like: FTRACE_DEFAULT_OFF(__ppc64_runlatch_on); That adds the function to a different section that places it into another file that keeps it from being traced, but can be enabled when you want it to. -- Steve