From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753702AbYI1RNR (ORCPT ); Sun, 28 Sep 2008 13:13:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752431AbYI1RNH (ORCPT ); Sun, 28 Sep 2008 13:13:07 -0400 Received: from ug-out-1314.google.com ([66.249.92.172]:41985 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752371AbYI1RNG (ORCPT ); Sun, 28 Sep 2008 13:13:06 -0400 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=p9Eoo0XuILd1v01dL2p3wtFDbsq5S3R/1kXpd5kRqYNcbjKLE0mVm4q8Z4eNAA2Dj0 CRMlY/vexpM9Eb/4v1xeqz4bmDhERJmepXKkBoU1Ujul/uGd7jQfehD6KRe8Pfa/x581 Po2cUzmmvZ7o/k+TRnETBd9FTfBNERJEFkhCc= Date: Sun, 28 Sep 2008 20:12:59 +0300 From: Pekka Paalanen To: "=?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker" Cc: mingo@elte.hu, rostedt@goodmis.org, linux-kernel@vger.kernel.org Subject: trace_pipe tentative fix (Re: [PATCH -tip 2/3] Tracing/ftrace: Adapt mmiotrace to the new type of print_line) Message-ID: <20080928201259.09bbac54@daedalus.pq.iki.fi> In-Reply-To: References: <48DD0347.5070008@gmail.com> <20080927002121.0038cdfe@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 Sat, 27 Sep 2008 14:17:47 +0200 "Frédéric Weisbecker" wrote: > 2008/9/26 Pekka Paalanen : > > Yes, I do disagree about printing stuff that doesn't belong there. > > First, I doubt printing bogus text is a right way to fix the > > early pipe EOF problem. Second, if you really have to do that, > > do it so that it obeys the mmiotrace log format specification. > > (I'd recommend a MARK entry.) The spec is in > > Documentation/tracers/mmiotrace.txt. > > No problem, I have one other option: ignoring and sleep again before > receiving another entries. > I can do another patch this week end to implement that. > The third patch only concerns the boot tracer. It relays to other > output functions. > > Just tell me if you agree with the ignoring... If I understand you suggestion, it looks like the right thing to do. Here is a tentative fix, which has not even been compile-tested. Is it so that the problem is triggered by consuming a trace entry which does not produce any output? If that entry is all there is in the ring at a time of a read call, then the last call to trace_seq_to_user() returns -EBUSY, because there is nothing to copy to user. What I failed to understand when I wrote that piece of code, is that returning 0 means EOF. The only cases when we do want to return an EOF are near the while (trace_empty(iter)) { loop. Frederic, could you test the fix, and if it works, send it to Ingo? Thanks. --- diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 6ada059..d85659a 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2616,6 +2616,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, goto out; } +waitagain: while (trace_empty(iter)) { if ((filp->f_flags & O_NONBLOCK)) { @@ -2749,8 +2750,13 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, sret = trace_seq_to_user(&iter->seq, ubuf, cnt); if (iter->seq.readpos >= iter->seq.len) trace_seq_reset(&iter->seq); + + /* + * If there was nothing to send to user, inspite of consuming trace + * entries, go back to wait for more entries. + */ if (sret == -EBUSY) - sret = 0; + goto waitagain; out: mutex_unlock(&trace_types_lock);