rcutorture: Make torture.sh --do-rt use CONFIG_PREEMPT_RT

The torture.sh --do-rt command-line parameter is intended to mimic -rt
kernels.  Now that CONFIG_PREEMPT_RT is upstream, this commit makes this
mimicking more precise.

Note that testing of RCU priority boosting is disabled in favor
of forward-progress testing of RCU callbacks.  If it turns out to be
possible to make kernels built with CONFIG_PREEMPT_RT=y to tolerate
testing of both, both will be enabled.

[ paulmck: Apply Sebastian Siewior feedback. ]

Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Joel Fernandes <[email protected]>

Author: paulmckrcu

tools/testing/selftests/rcutorture/bin/torture.sh

@@ -448,13 +448,17 @@ fi
 
 if test "$do_rt" = "yes"
 then
-	# With all post-boot grace periods forced to normal.
-	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 rcupdate.rcu_normal=1"
-	torture_set "rcurttorture" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration "$duration_rcutorture" --configs "TREE03" --trust-make
+	# In both runs, disable testing of RCU priority boosting because
+	# -rt doesn't like its interaction with testing of callback
+	# flooding.
+
+	# With all post-boot grace periods forced to normal (default for PREEMPT_RT).
+	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 rcutorture.test_boost=0 rcutorture.preempt_duration=0"
+	torture_set "rcurttorture" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration "$duration_rcutorture" --configs "TREE03" --kconfig "CONFIG_PREEMPT_RT=y CONFIG_EXPERT=y CONFIG_HZ_PERIODIC=n CONFIG_NO_HZ_IDLE=y CONFIG_RCU_NOCB_CPU=y" --trust-make
 
 	# With all post-boot grace periods forced to expedited.
-	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 rcupdate.rcu_expedited=1"
-	torture_set "rcurttorture-exp" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration "$duration_rcutorture" --configs "TREE03" --trust-make
+	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 rcutorture.test_boost=0 rcupdate.rcu_normal_after_boot=0 rcupdate.rcu_expedited=1 rcutorture.preempt_duration=0"
+	torture_set "rcurttorture-exp" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration "$duration_rcutorture" --configs "TREE03" --kconfig "CONFIG_PREEMPT_RT=y CONFIG_EXPERT=y CONFIG_HZ_PERIODIC=n CONFIG_NO_HZ_FULL=y CONFIG_RCU_NOCB_CPU=y" --trust-make
 fi
 
 if test "$do_srcu_lockdep" = "yes"