From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752637AbYKXV1f (ORCPT ); Mon, 24 Nov 2008 16:27:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752392AbYKXV12 (ORCPT ); Mon, 24 Nov 2008 16:27:28 -0500 Received: from gv-out-0910.google.com ([216.239.58.188]:5958 "EHLO gv-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750913AbYKXV11 (ORCPT ); Mon, 24 Nov 2008 16:27:27 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:in-reply-to:references:x-mailer :mime-version:content-type:content-transfer-encoding:sender; b=CDwSHQlk5iSrMbueFWk5oiofMnRg/0UWS3z6ax7OJg8BjoKIXvEgkawTC6evviXjub bVnCz0/vcgNyrzzn4zIYPA5nbIpSLZ6GWExz3TAvPB+THADe8bx2ArSXDhUF5P55ZiyD s0ZrYWmR6FWW/CQyXlxrIBTfNfEYtvQmUFVzA= Date: Mon, 24 Nov 2008 23:27:20 +0200 From: Pekka Paalanen To: "=?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker" Cc: "Ingo Molnar" , "Steven Rostedt" , linux-kernel Subject: Re: [PATCH 1/2] mmiotrace: fix buffer overrun detection Message-ID: <20081124232720.59312c0d@daedalus.pq.iki.fi> In-Reply-To: References: <20081123154148.04e0851a@daedalus.pq.iki.fi> <20081123212430.4f6700e9@daedalus.pq.iki.fi> <20081123193413.GB2794@elte.hu> <20081124221849.33c91bcf@daedalus.pq.iki.fi> X-Mailer: Claws Mail 3.5.0 (GTK+ 2.12.11; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 24 Nov 2008 21:30:24 +0100 "Frédéric Weisbecker" wrote: > 2008/11/24 Pekka Paalanen : > > > > Oh right, the busylooping bug when echoing into trace_marker, > > I already forgot about that, since I couldn't reproduce it. > > I guess there's nothing to do, until someone finds a way to > > reproduce it. > > > Hi Pekka. > > Are you talking about this old bug that broke the pipe? > If so, you fixed it yourself partially with a patch that corrected > tracing_read_pipe. > Another origin was the none tracer that set tracer_enabled to 0. > But i has been fixed with the nop tracer. > > Perhaps you are talking of something else? Yeah, I'm talking about the shell spinning 90% in kernel and 10% in user, I tried to explain it in the part you left out from the quote. That is, doing 'echo foo > trace_marker' makes the shell/echo spin. And this doesn't seem to be deterministic, or the exact triggering sequence is too complex. I didn't notice any other adverse effects than the shell getting stuck. Maybe a corner case related to having only a single page in the ring buffer... nah, more likely something unexpected under trace_marker callbacks. Returning zero instead of error on write(2) maybe... something that makes 'echo' retry again and again, never succeeding or really failing. -- Pekka Paalanen http://www.iki.fi/pq/