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Subject[PATCH 5.4 039/102] perf map: No need to adjust the long name of modules
Date
From: Arnaldo Carvalho de Melo <acme@redhat.com>

commit f068435d9bb2d825d59e3c101bc579f09315ee01 upstream.

At some point in the past we needed to make sure we would get the long
name of modules and not just what we get from /proc/modules, but that
need, as described in the cset that introduced the adjustment function:

Fixes: c03d5184f0e9 ("perf machine: Adjust dso->long_name for offline module")

Without using the buildid-cache:

# lsmod | grep trusted
# insmod trusted.ko
# lsmod | grep trusted
trusted 24576 0
# strace -e open,openat perf probe -m ./trusted.ko key_seal |& grep trusted
openat(AT_FDCWD, "/sys/module/trusted/notes/.note.gnu.build-id", O_RDONLY) = 4
openat(AT_FDCWD, "/sys/module/trusted/notes/.note.gnu.build-id", O_RDONLY) = 7
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
openat(AT_FDCWD, "/root/.debug/root/trusted.ko/dd3d355d567394d540f527e093e0f64b95879584/probes", O_RDWR|O_CREAT, 0644) = 3
openat(AT_FDCWD, "/usr/lib/debug/root/trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/debug/root/trusted.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/root/.debug/trusted.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
openat(AT_FDCWD, "trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, ".debug/trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 4
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
probe:key_seal (on key_seal in trusted)
# perf probe -l
probe:key_seal (on key_seal in trusted)
#

No attempt at opening '[trusted]'.

Now using the build-id cache:

# rmmod trusted
# perf buildid-cache --add ./trusted.ko
# insmod trusted.ko
# strace -e open,openat perf probe -m ./trusted.ko key_seal |& grep trusted
openat(AT_FDCWD, "/sys/module/trusted/notes/.note.gnu.build-id", O_RDONLY) = 4
openat(AT_FDCWD, "/sys/module/trusted/notes/.note.gnu.build-id", O_RDONLY) = 7
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
openat(AT_FDCWD, "/root/.debug/root/trusted.ko/dd3d355d567394d540f527e093e0f64b95879584/probes", O_RDWR|O_CREAT, 0644) = 3
openat(AT_FDCWD, "/usr/lib/debug/root/trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/debug/root/trusted.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/root/.debug/trusted.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
openat(AT_FDCWD, "trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, ".debug/trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 4
openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
#

Again, no attempt at reading '[trusted]'.

Finally, adding a probe to that function and then using:

[root@quaco ~]# perf trace -e probe_perf:*/max-stack=16/ --max-events=2
0.000 perf/13456 probe_perf:dso__adjust_kmod_long_name(__probe_ip: 5492263)
dso__adjust_kmod_long_name (/home/acme/bin/perf)
machine__process_kernel_mmap_event (/home/acme/bin/perf)
machine__process_mmap_event (/home/acme/bin/perf)
perf_event__process_mmap (/home/acme/bin/perf)
machines__deliver_event (/home/acme/bin/perf)
perf_session__deliver_event (/home/acme/bin/perf)
perf_session__process_event (/home/acme/bin/perf)
process_simple (/home/acme/bin/perf)
reader__process_events (/home/acme/bin/perf)
__perf_session__process_events (/home/acme/bin/perf)
perf_session__process_events (/home/acme/bin/perf)
process_buildids (/home/acme/bin/perf)
record__finish_output (/home/acme/bin/perf)
__cmd_record (/home/acme/bin/perf)
cmd_record (/home/acme/bin/perf)
run_builtin (/home/acme/bin/perf)
0.055 perf/13456 probe_perf:dso__adjust_kmod_long_name(__probe_ip: 5492263)
dso__adjust_kmod_long_name (/home/acme/bin/perf)
machine__process_kernel_mmap_event (/home/acme/bin/perf)
machine__process_mmap_event (/home/acme/bin/perf)
perf_event__process_mmap (/home/acme/bin/perf)
machines__deliver_event (/home/acme/bin/perf)
perf_session__deliver_event (/home/acme/bin/perf)
perf_session__process_event (/home/acme/bin/perf)
process_simple (/home/acme/bin/perf)
reader__process_events (/home/acme/bin/perf)
__perf_session__process_events (/home/acme/bin/perf)
perf_session__process_events (/home/acme/bin/perf)
process_buildids (/home/acme/bin/perf)
record__finish_output (/home/acme/bin/perf)
__cmd_record (/home/acme/bin/perf)
cmd_record (/home/acme/bin/perf)
run_builtin (/home/acme/bin/perf)
#

This was the only path I could find using the perf tools that reach at this
function, then as of november/2019, if we put a probe in the line where the
actuall setting of the dso->long_name is done:

# perf trace -e probe_perf:*
^C[root@quaco ~]
# perf stat -e probe_perf:* -I 2000
2.000404265 0 probe_perf:dso__adjust_kmod_long_name
4.001142200 0 probe_perf:dso__adjust_kmod_long_name
6.001704120 0 probe_perf:dso__adjust_kmod_long_name
8.002398316 0 probe_perf:dso__adjust_kmod_long_name
10.002984010 0 probe_perf:dso__adjust_kmod_long_name
12.003597851 0 probe_perf:dso__adjust_kmod_long_name
14.004113303 0 probe_perf:dso__adjust_kmod_long_name
16.004582773 0 probe_perf:dso__adjust_kmod_long_name
18.005176373 0 probe_perf:dso__adjust_kmod_long_name
20.005801605 0 probe_perf:dso__adjust_kmod_long_name
22.006467540 0 probe_perf:dso__adjust_kmod_long_name
^C 23.683261941 0 probe_perf:dso__adjust_kmod_long_name

#

Its not being used at all.

To further test this I used kvm.ko as the offline module, i.e. removed
if from the buildid-cache by nuking it completely (rm -rf ~/.debug) and
moved it from the normal kernel distro path, removed the modules, stoped
the kvm guest, and then installed it manually, etc.

# rmmod kvm-intel
# rmmod kvm
# lsmod | grep kvm
# modprobe kvm-intel
modprobe: ERROR: ctx=0x55d3b1722260 path=/lib/modules/5.3.8-200.fc30.x86_64/kernel/arch/x86/kvm/kvm.ko.xz error=No such file or directory
modprobe: ERROR: ctx=0x55d3b1722260 path=/lib/modules/5.3.8-200.fc30.x86_64/kernel/arch/x86/kvm/kvm.ko.xz error=No such file or directory
modprobe: ERROR: could not insert 'kvm_intel': Unknown symbol in module, or unknown parameter (see dmesg)
# insmod ./kvm.ko
# modprobe kvm-intel
modprobe: ERROR: ctx=0x562f34026260 path=/lib/modules/5.3.8-200.fc30.x86_64/kernel/arch/x86/kvm/kvm.ko.xz error=No such file or directory
modprobe: ERROR: ctx=0x562f34026260 path=/lib/modules/5.3.8-200.fc30.x86_64/kernel/arch/x86/kvm/kvm.ko.xz error=No such file or directory
# lsmod | grep kvm
kvm_intel 299008 0
kvm 765952 1 kvm_intel
irqbypass 16384 1 kvm
#
# perf probe -x ~/bin/perf machine__findnew_module_map:12 mname=m.name:string filename=filename:string 'dso_long_name=map->dso->long_name:string' 'dso_name=map->dso->name:string'
# perf probe -l
probe_perf:machine__findnew_module_map (on machine__findnew_module_map:12@util/machine.c in /home/acme/bin/perf with mname filename dso_long_name dso_name)
# perf record
^C[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 3.416 MB perf.data (33956 samples) ]
# perf trace -e probe_perf:machine*
<SNIP>
6.322 perf/23099 probe_perf:machine__findnew_module_map(__probe_ip: 5492493, mname: "[salsa20_generic]", filename: "/lib/modules/5.3.8-200.fc30.x86_64/kernel/crypto/salsa20_generic.ko.xz", dso_long_name: "/lib/modules/5.3.8-200.fc30.x86_64/kernel/crypto/salsa20_generic.ko.xz", dso_name: "[salsa20_generic]")
6.375 perf/23099 probe_perf:machine__findnew_module_map(__probe_ip: 5492493, mname: "[kvm]", filename: "[kvm]", dso_long_name: "[kvm]", dso_name: "[kvm]")
<SNIP>

The filename doesn't come with the path, no point in trying to set the dso->long_name.

[root@quaco ~]# strace -e open,openat perf probe -m ./kvm.ko kvm_apic_local_deliver |& egrep 'open.*kvm'
openat(AT_FDCWD, "/sys/module/kvm_intel/notes/.note.gnu.build-id", O_RDONLY) = 4
openat(AT_FDCWD, "/sys/module/kvm/notes/.note.gnu.build-id", O_RDONLY) = 4
openat(AT_FDCWD, "/lib/modules/5.3.8-200.fc30.x86_64/kernel/arch/x86/kvm", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 7
openat(AT_FDCWD, "/sys/module/kvm_intel/notes/.note.gnu.build-id", O_RDONLY) = 8
openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 3
openat(AT_FDCWD, "/root/.debug/root/kvm.ko/5955f426cb93f03f30f3e876814be2db80ab0b55/probes", O_RDWR|O_CREAT, 0644) = 3
openat(AT_FDCWD, "/usr/lib/debug/root/kvm.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/debug/root/kvm.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/root/.debug/kvm.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 3
openat(AT_FDCWD, "kvm.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, ".debug/kvm.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "kvm.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 3
openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 3
openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 4
openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 3
[root@quaco ~]#

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-jlfew3lyb24d58egrp0o72o2@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
tools/perf/util/machine.c | 27 +--------------------------
1 file changed, 1 insertion(+), 26 deletions(-)

--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -767,24 +767,6 @@ int machine__process_ksymbol(struct mach
return machine__process_ksymbol_register(machine, event, sample);
}

-static void dso__adjust_kmod_long_name(struct dso *dso, const char *filename)
-{
- const char *dup_filename;
-
- if (!filename || !dso || !dso->long_name)
- return;
- if (dso->long_name[0] != '[')
- return;
- if (!strchr(filename, '/'))
- return;
-
- dup_filename = strdup(filename);
- if (!dup_filename)
- return;
-
- dso__set_long_name(dso, dup_filename, true);
-}
-
struct map *machine__findnew_module_map(struct machine *machine, u64 start,
const char *filename)
{
@@ -796,15 +778,8 @@ struct map *machine__findnew_module_map(
return NULL;

map = map_groups__find_by_name(&machine->kmaps, m.name);
- if (map) {
- /*
- * If the map's dso is an offline module, give dso__load()
- * a chance to find the file path of that module by fixing
- * long_name.
- */
- dso__adjust_kmod_long_name(map->dso, filename);
+ if (map)
goto out;
- }

dso = machine__findnew_module_dso(machine, &m, filename);
if (dso == NULL)

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