Messages in this thread | | | Date | Mon, 29 Sep 2008 19:49:46 +0200 | From | "Frédéric Weisbecker" <> | Subject | Re: trace_pipe tentative fix |
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2008/9/28 Pekka Paalanen <pq@iki.fi>: > On Sun, 28 Sep 2008 20:12:59 +0300 > Pekka Paalanen <pq@iki.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); >
Tested! And, no problem as far as I can see :) So I'm going to send the new patchset.
Thanks.
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