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From: "dsmith at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: systemtap@sourceware.org
Subject: [Bug translator/19396] systemtap can't find certain kernel tracepoints
Date: Wed, 06 Jan 2016 17:12:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D19396

--- Comment #1 from David Smith <dsmith at redhat dot com> ---
I'm seeing something wacky here. This is on 2.6.32-573.el6.ppc64:

=3D=3D=3D=3D
# stap --poison-cache -L 'kernel.trace("*module*")'
kernel.trace("jbd:module_free") $mod:struct module*
kernel.trace("jbd:module_get") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("jbd:module_load") $mod:struct module*
kernel.trace("jbd:module_put") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("jbd:module_request") $name:char* $wait:bool $ip:long unsigned=
 int
=3D=3D=3D=3D

So, when '--poison-cache' is used, for some reason stap thinks the module_*
tracepoints are in the "jbd" subsystem instead of in the "module" subsystem.
But, you can list them as being in the "module" subsystem:

=3D=3D=3D=3D
# stap -L 'kernel.trace("*module*")'
kernel.trace("module:module_free") $mod:struct module*
kernel.trace("module:module_get") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("module:module_load") $mod:struct module*
kernel.trace("module:module_put") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("module:module_request") $name:char* $wait:bool $ip:long unsig=
ned
int
=3D=3D=3D=3D

You can actually see them in either subsystem:

=3D=3D=3D=3D
# stap -L 'kernel.trace("jbd:module*")'
kernel.trace("jbd:module_free") $mod:struct module*
kernel.trace("jbd:module_get") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("jbd:module_load") $mod:struct module*
kernel.trace("jbd:module_put") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("jbd:module_request") $name:char* $wait:bool $ip:long unsigned=
 int
# stap -L 'kernel.trace("module:module*")'
kernel.trace("module:module_free") $mod:struct module*
kernel.trace("module:module_get") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("module:module_load") $mod:struct module*
kernel.trace("module:module_put") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("module:module_request") $name:char* $wait:bool $ip:long unsig=
ned
int
=3D=3D=3D=3D

Note that if you try this with a completely non-existing subsystem, you do =
get
the correct result (of nothing):

=3D=3D=3D=3D
# stap -L 'kernel.trace("foo:module*")'
#
=3D=3D=3D=3D

It looks like you can look up the module tracepoints in about any (existing)
subsystem:

=3D=3D=3D=3D
# stap -L 'kernel.trace("ext4:module*")'
kernel.trace("ext4:module_free") $mod:struct module*
kernel.trace("ext4:module_get") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("ext4:module_load") $mod:struct module*
kernel.trace("ext4:module_put") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("ext4:module_request") $name:char* $wait:bool $ip:long unsigned
int
# stap -L 'kernel.trace("skb:module*")'
kernel.trace("skb:module_free") $mod:struct module*
kernel.trace("skb:module_get") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("skb:module_load") $mod:struct module*
kernel.trace("skb:module_put") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("skb:module_request") $name:char* $wait:bool $ip:long unsigned=
 int
# stap -L 'kernel.trace("net:module*")'
kernel.trace("net:module_free") $mod:struct module*
kernel.trace("net:module_get") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("net:module_load") $mod:struct module*
kernel.trace("net:module_put") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("net:module_request") $name:char* $wait:bool $ip:long unsigned=
 int
# stap -L 'kernel.trace("block:module*")'=20
kernel.trace("block:module_free") $mod:struct module*
kernel.trace("block:module_get") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("block:module_load") $mod:struct module*
kernel.trace("block:module_put") $mod:struct module* $ip:long unsigned int
$refcnt:int
kernel.trace("block:module_request") $name:char* $wait:bool $ip:long unsign=
ed
int
=3D=3D=3D=3D

Also note this isn't just because I used a wildcard, since the following wo=
rks:

=3D=3D=3D=3D
# stap -L 'kernel.trace("block:module_free")'
kernel.trace("block:module_free") $mod:struct module*
=3D=3D=3D=3D

--=20
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