LKML Archive on
help / color / mirror / Atom feed
From: Pekka Paalanen <>
To: Steven Rostedt <>
Cc: Ingo Molnar <>,
Subject: Re: tracing and mmiotrace
Date: Sun, 23 Mar 2008 13:01:33 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Sat, 22 Mar 2008 16:16:48 -0400 (EDT)
Steven Rostedt <> wrote:

> On Sat, 22 Mar 2008, Pekka Paalanen wrote:
> > First you see my check in __trace_special() trigger, and then NULL
> > pointer dereference BUG at ffffffff80259332 which translates to
> > kernel/trace/trace.c:639 in tracing_generic_entry_update(), line:
> > 	entry->preempt_count	= pc & 0xff;
> > I don't understand why it tries to dereference NULL even when I
> > check for it.
> Interesting. I'll have to look into that more on Monday.

I found the culprit.

My code never calls tracing_reset(). If I had enabled
FTRACE_STARTUP_TEST, the selftest code would run tracing_reset().
So I copied stack_reset() from trace_sysprof.c and now recording works.
My bad.

btw. the semantics of verbose iter_ctrl seem inverted from user point
of view. I also noticed that 'trace' file does not consume the data and
'trace_pipe' does consume the data. This is important information for the

I think it would be nice, if iter_ctrl listed only the flags the current
tracer supports. This would also imply, that the tracer is not started
automatically when selected. Most of the flags are not useful for


Pekka Paalanen

  reply	other threads:[~2008-03-23 11:01 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
     [not found] ` <>
2008-03-22 15:32   ` Pekka Paalanen
2008-03-22 20:16     ` Steven Rostedt
2008-03-23 11:01       ` Pekka Paalanen [this message]
2008-03-23 17:16       ` Pekka Paalanen
2008-03-30 18:12         ` Pekka Paalanen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \
    --subject='Re: tracing and mmiotrace' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).