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Date: Sun, 28 Sep 2008 21:58:15 +0300 From: Pekka Paalanen <pq@....fi> To: "Frédéric Weisbecker" <fweisbec@...il.com> Cc: mingo@...e.hu, rostedt@...dmis.org, linux-kernel@...r.kernel.org Subject: Re: trace_pipe tentative fix On Sun, 28 Sep 2008 20:12:59 +0300 Pekka Paalanen <pq@....fi> 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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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