Patch "ftrace/selftests: workaround cgroup RT scheduling issues" has been added to the 5.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    ftrace/selftests: workaround cgroup RT scheduling issues

to the 5.6-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:
     ftrace-selftests-workaround-cgroup-rt-scheduling-iss.patch
and it can be found in the queue-5.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 9ab5c0e3dc7ab97b9b432d237bd3cb7f1da80c00
Author: Alan Maguire <alan.maguire@xxxxxxxxxx>
Date:   Wed Feb 19 09:33:29 2020 +0000

    ftrace/selftests: workaround cgroup RT scheduling issues
    
    [ Upstream commit 57c4cfd4a2eef8f94052bd7c0fce0981f74fb213 ]
    
    wakeup_rt.tc and wakeup.tc tests in tracers/ subdirectory
    fail due to the chrt command returning:
    
     chrt: failed to set pid 0's policy: Operation not permitted.
    
    To work around this, temporarily disable grout RT scheduling
    during ftracetest execution.  Restore original value on
    test run completion.  With these changes in place, both
    tests consistently pass.
    
    Fixes: c575dea2c1a5 ("selftests/ftrace: Add wakeup_rt tracer testcase")
    Fixes: c1edd060b413 ("selftests/ftrace: Add wakeup tracer testcase")
    Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
    Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
    Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/testing/selftests/ftrace/ftracetest b/tools/testing/selftests/ftrace/ftracetest
index 063ecb290a5a3..144308a757b70 100755
--- a/tools/testing/selftests/ftrace/ftracetest
+++ b/tools/testing/selftests/ftrace/ftracetest
@@ -29,8 +29,25 @@ err_ret=1
 # kselftest skip code is 4
 err_skip=4
 
+# cgroup RT scheduling prevents chrt commands from succeeding, which
+# induces failures in test wakeup tests.  Disable for the duration of
+# the tests.
+
+readonly sched_rt_runtime=/proc/sys/kernel/sched_rt_runtime_us
+
+sched_rt_runtime_orig=$(cat $sched_rt_runtime)
+
+setup() {
+  echo -1 > $sched_rt_runtime
+}
+
+cleanup() {
+  echo $sched_rt_runtime_orig > $sched_rt_runtime
+}
+
 errexit() { # message
   echo "Error: $1" 1>&2
+  cleanup
   exit $err_ret
 }
 
@@ -39,6 +56,8 @@ if [ `id -u` -ne 0 ]; then
   errexit "this must be run by root user"
 fi
 
+setup
+
 # Utilities
 absdir() { # file_path
   (cd `dirname $1`; pwd)
@@ -235,6 +254,7 @@ TOTAL_RESULT=0
 
 INSTANCE=
 CASENO=0
+
 testcase() { # testfile
   CASENO=$((CASENO+1))
   desc=`grep "^#[ \t]*description:" $1 | cut -f2 -d:`
@@ -406,5 +426,7 @@ prlog "# of unsupported: " `echo $UNSUPPORTED_CASES | wc -w`
 prlog "# of xfailed: " `echo $XFAILED_CASES | wc -w`
 prlog "# of undefined(test bug): " `echo $UNDEFINED_CASES | wc -w`
 
+cleanup
+
 # if no error, return 0
 exit $TOTAL_RESULT