torture: Provide bare-metal modprobe-based advice

torture: Provide bare-metal modprobe-based advice

In some environments, the torture-testing use of virtualization is
inconvenient.  In such cases, the modprobe and rmmod commands may be used
to do torture testing, but significant setup is required to build, boot,
and modprobe a kernel so as to match a given torture-test scenario.
This commit therefore creates a "bare-metal" file in each results
directory containing steps to run the corresponding scenario using the
modprobe command on bare metal.  For example, the contents of this file
after using kvm.sh to build an rcutorture TREE01 kernel, perhaps with
the --buildonly argument, is as follows:

To run this scenario on bare metal:

 1. Set your bare-metal build tree to the state shown in this file:
    /home/git/linux-rcu/tools/testing/selftests/rcutorture/res/2021.02.04-17.10.19/testid.txt
 2. Update your bare-metal build tree's .config based on this file:
    /home/git/linux-rcu/tools/testing/selftests/rcutorture/res/2021.02.04-17.10.19/TREE01/ConfigFragment
 3. Make the bare-metal kernel's build system aware of your .config updates:
    $ yes "" | make oldconfig
 4. Build your bare-metal kernel.
 5. Boot your bare-metal kernel with the following parameters:
    maxcpus=8 nr_cpus=43 rcutree.gp_preinit_delay=3 rcutree.gp_init_delay=3 rcutree.gp_cleanup_delay=3 rcu_nocbs=0-1,3-7
 6. Start the test with the following command:
    $ modprobe rcutorture nocbs_nthreads=8 nocbs_toggle=1000 fwd_progress=0 onoff_interval=1000 onoff_holdoff=30 n_barrier_cbs=4 stat_interval=15 shutdown_secs=120 test_no_idle_hz=1 verbose=1
 7. After some time, end the test with the following command:
    $ rmmod rcutorture
 8. Copy your bare-metal kernel's .config file, overwriting this file:
    /home/git/linux-rcu/tools/testing/selftests/rcutorture/res/2021.02.04-17.10.19/TREE01/.config
 9. Copy the console output from just before the modprobe to just after
    the rmmod into this file:
    /home/git/linux-rcu/tools/testing/selftests/rcutorture/res/2021.02.04-17.10.19/TREE01/console.log
10. Check for runtime errors using the following command:
   $ tools/testing/selftests/rcutorture/bin/kvm-recheck.sh /home/git/linux-rcu/tools/testing/selftests/rcutorture/res/2021.02.04-17.10.19

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>