[PATCH] Marker depmod fix core kernel list

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

* Theodore Ts'o (tytso@mit.edu) wrote:
> 
> I've been playing with adding some markers into ext4 to see if they
> could be useful in solving some problems along with Systemtap.  It
> appears, though, that as of 2.6.27-rc8, markers defined in code which is
> compiled directly into the kernel (i.e., not as modules) don't show up
> in Module.markers:
> 
> kvm_trace_entryexit arch/x86/kvm/kvm-intel  %u %p %u %u %u %u %u %u
> kvm_trace_handler arch/x86/kvm/kvm-intel  %u %p %u %u %u %u %u %u
> kvm_trace_entryexit arch/x86/kvm/kvm-amd  %u %p %u %u %u %u %u %u
> kvm_trace_handler arch/x86/kvm/kvm-amd  %u %p %u %u %u %u %u %u
> 
> (Note the lack of any of the kernel_sched_* markers, and the markers I
> added for ext4_* and jbd2_* are missing as wel.)
> 
> Systemtap apparently depends on in-kernel trace_mark being recorded in
> Module.markers, and apparently it's been claimed that it used to be
> there.  Is this a bug in systemtap, or in how Module.markers is getting
> built?   And is there a file that contains the equivalent information
> for markers located in non-modules code?
> 
> Thanks, regards,
> 


I think the problem comes from this patch :
commit d35cb360c29956510b2fe1a953bd4968536f7216
"markers: fix duplicate modpost entry"

Especially :

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index a07f91a..8f038e6 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1992,7 +1992,8 @@ static void read_markers(const char *fname)
      mod->skip = 1;
    }

-   add_marker(mod, marker, fmt);
+   if (!mod->skip)
+     add_marker(mod, marker, fmt);
  }
  return;
 fail:

Here is a fix that should take care if this problem. Given I am not the
modpost expert, let's see if I can get an ACK from Sam.

Thanks for the bug report!

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Theodore Ts'o <tytso@mit.edu>
CC: David Smith <dsmith@redhat.com>
CC: Roland McGrath <roland@redhat.com>
CC: Sam Ravnborg <sam@ravnborg.org>
CC: Wenji Huang <wenji.huang@oracle.com>
CC: Takashi Nishiie <t-nishiie@np.css.fujitsu.com>
---
 scripts/mod/modpost.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Index: linux-2.6-lttng/scripts/mod/modpost.c
===================================================================
--- linux-2.6-lttng.orig/scripts/mod/modpost.c	2008-10-03 15:42:00.000000000 -0400
+++ linux-2.6-lttng/scripts/mod/modpost.c	2008-10-03 15:42:59.000000000 -0400
@@ -1986,11 +1986,13 @@ static void read_markers(const char *fna
 
 		mod = find_module(modname);
 		if (!mod) {
-			if (is_vmlinux(modname))
-				have_vmlinux = 1;
 			mod = new_module(NOFAIL(strdup(modname)));
 			mod->skip = 1;
 		}
+		if (is_vmlinux(modname)) {
+			have_vmlinux = 1;
+			mod->skip = 0;
+		}
 
 		if (!mod->skip)
 			add_marker(mod, marker, fmt);

-- 
Mathieu Desnoyers
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