Patch "perf header: Fixup reading of HEADER_NRCPUS feature" has been added to the 4.2-stable tree

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

perf header: Fixup reading of HEADER_NRCPUS feature

to the 4.2-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-fixup-reading-of-header_nrcpus-feature.patch
and it can be found in the queue-4.2 subdirectory.

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

From: Arnaldo Carvalho de Melo <[email protected]>
Date: Fri, 11 Sep 2015 12:36:12 -0300
Subject: perf header: Fixup reading of HEADER_NRCPUS feature

From: Arnaldo Carvalho de Melo <[email protected]>

commit caa470475d9b59eeff093ae650800d34612c4379 upstream.

The original patch introducing this header wrote the number of CPUs available and online in one order and then swapped those values when reading, fix it.

Before:

  # perf record usleep 1
  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 4
  # nrcpus avail : 4
  # echo 0 > /sys/devices/system/cpu/cpu2/online
  # perf record usleep 1
  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 4
  # nrcpus avail : 3
  # echo 0 > /sys/devices/system/cpu/cpu1/online
  # perf record usleep 1
  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 4
  # nrcpus avail : 2

After the fix, bringing back the CPUs online:

  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 2
  # nrcpus avail : 4
  # echo 1 > /sys/devices/system/cpu/cpu2/online
  # perf record usleep 1
  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 3
  # nrcpus avail : 4
  # echo 1 > /sys/devices/system/cpu/cpu1/online
  # perf record usleep 1
  # perf report --header-only | grep 'nrcpus \(online\|avail\)'
  # nrcpus online : 4
  # nrcpus avail : 4

---
 tools/perf/util/header.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -1442,7 +1442,7 @@ static int process_nrcpus(struct perf_fi
 	if (ph->needs_swap)
 		nr = bswap_32(nr);
 
-	ph->env.nr_cpus_online = nr;
+	ph->env.nr_cpus_avail = nr;
 
 	ret = readn(fd, &nr, sizeof(nr));
 	if (ret != sizeof(nr))

@@ -1451,7 +1451,7 @@ static int process_nrcpus(struct perf_fi
 	if (ph->needs_swap)
 		nr = bswap_32(nr);
 
-	ph->env.nr_cpus_avail = nr;
+	ph->env.nr_cpus_online = nr;
 	return 0;
 }
 

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

queue-4.2/perf-tools-add-empty-build-files-for-architectures-lacking-them.patch queue-4.2/perf-stat-get-correct-cpu-id-for-print_aggr.patch queue-4.2/perf-probe-use-existing-routine-to-look-for-a-kernel-module-by-dso-short_name.patch queue-4.2/perf-tools-add-missing-forward-declaration-of-struct-map-to-probe-event.h.patch queue-4.2/perf-tools-fix-copying-of-proc-kcore.patch queue-4.2/perf-hists-update-the-column-width-for-the-srcline-sort-key.patch queue-4.2/perf-tools-fix-parse_events_add_pmu-caller.patch queue-4.2/perf-header-fixup-reading-of-header_nrcpus-feature.patch