From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753042AbYI1S6a (ORCPT ); Sun, 28 Sep 2008 14:58:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751152AbYI1S6W (ORCPT ); Sun, 28 Sep 2008 14:58:22 -0400 Received: from ug-out-1314.google.com ([66.249.92.169]:42857 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751120AbYI1S6W (ORCPT ); Sun, 28 Sep 2008 14:58:22 -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=b1v5IuuX3FsttsNJ2YRwzMImoyjb3J/LYSHCW61DnOgp3rs2Dpvab02z1bl1NMGGi9 1g7K2lbyW7C4DKPGWMiw5cGtqi/TtamAnp8th9R+hKYamc3eJh3eszisn2YVdKlQmFGe OxaIES6C+rh+qe2RNURnCjUglXwGirLXJ/4g0= Date: Sun, 28 Sep 2008 21:58:15 +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: Re: trace_pipe tentative fix Message-ID: <20080928215815.3a9aa355@daedalus.pq.iki.fi> In-Reply-To: <20080928201259.09bbac54@daedalus.pq.iki.fi> References: <48DD0347.5070008@gmail.com> <20080927002121.0038cdfe@daedalus.pq.iki.fi> <20080928201259.09bbac54@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=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 28 Sep 2008 20:12:59 +0300 Pekka Paalanen wrote: > 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? Whoops, sret was left in a bad state. Here's a new one. --- diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 6ada059..16b8a22 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2605,7 +2605,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, sret = trace_seq_to_user(&iter->seq, ubuf, cnt); if (sret != -EBUSY) return sret; - sret = 0; trace_seq_reset(&iter->seq); @@ -2616,6 +2615,8 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, goto out; } +waitagain: + sret = 0; 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);