Patch "perf header: Set proper module name when build-id event found" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

perf header: Set proper module name when build-id event found

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
perf-header-set-proper-module-name-when-build-id-event-found.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Namhyung Kim <[email protected]>
Date: Wed, 31 May 2017 21:01:03 +0900
Subject: perf header: Set proper module name when build-id event found

From: Namhyung Kim <[email protected]>

[ Upstream commit 1deec1bd96ccd8beb04d2112a6d12fe20505c3a6 ]

When perf processes build-id event, it creates DSOs with the build-id. But it didn't set the module short name (like '[module-name]') so when processing a kernel mmap event of the module, it cannot found the DSO as it only checks the short names.

That leads for perf to create a same DSO without the build-id info and it'll lookup the system path even if the DSO is already in the build-id cache. After kernel was updated, perf cannot find the DSO and cannot show symbols in it anymore.

You can see this if you have an old data file (w/ old kernel version):

  $ perf report -i perf.data.old -v |& grep scsi_mod
  build id event received for /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz : cafe1ce6ca13a98a5d9ed3425cde249e57a27fc1
  Failed to open /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz, continuing without symbols
  ...

The second message didn't show the build-id. With this patch:

  $ perf report -i perf.data.old -v |& grep scsi_mod
  build id event received for /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz: cafe1ce6ca13a98a5d9ed3425cde249e57a27fc1
  /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz with build id cafe1ce6ca13a98a5d9ed3425cde249e57a27fc1 not found, continuing without symbols
  ...

Now it shows the build-id but still cannot load the symbol table. This is a different problem which will be fixed in the next patch.

---
 tools/perf/util/header.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

@@ -1454,8 +1454,16 @@ static int __event_process_build_id(stru
 
 		dso__set_build_id(dso, &bev->build_id);
 
-		if (!is_kernel_module(filename, cpumode))
-			dso->kernel = dso_type;
+		if (dso_type != DSO_TYPE_USER) {
+			struct kmod_path m = { .name = NULL, };
+
+			if (!kmod_path__parse_name(&m, filename) && m.kmod)
+				dso__set_short_name(dso, strdup(m.name), true);
+			else
+				dso->kernel = dso_type;
+
+			free(m.name);
+		}
 
 		build_id__sprintf(dso->build_id, sizeof(dso->build_id),
 				  sbuild_id);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/perf-report-fix-off-by-one-for-non-activation-frames.patch queue-4.9/perf-trace-add-mmap-alias-for-s390.patch queue-4.9/perf-report-ensure-the-perf-dso-mapping-matches-what-libdw-sees.patch queue-4.9/perf-tools-fix-copyfile_offset-update-of-output-offset.patch queue-4.9/perf-tools-decompress-kernel-module-when-reading-dso-data.patch queue-4.9/perf-tests-decompress-kernel-module-before-objdump.patch queue-4.9/perf-header-set-proper-module-name-when-build-id-event-found.patch