linux-toradex.git/tools/testing/selftests/rcutorture/doc, branch master

rcu: Remove CONFIG_SRCU

2023-04-05T13:47:41+00:00

Now that all references to CONFIG_SRCU have been removed, it is time to
remove CONFIG_SRCU itself.

Signed-off-by: Paul E. McKenney 
Cc: John Ogness 
Cc: Petr Mladek 
Reviewed-by: John Ogness 
Signed-off-by: Joel Fernandes (Google)

rcu: Remove the RCU_FAST_NO_HZ Kconfig option

2021-12-01T01:24:47+00:00

All of the uses of CONFIG_RCU_FAST_NO_HZ=y that I have seen involve
systems with RCU callbacks offloaded.  In this situation, all that this
Kconfig option does is slow down idle entry/exit with an additional
allways-taken early exit.  If this is the only use case, then this
Kconfig option nothing but an attractive nuisance that needs to go away.

This commit therefore removes the RCU_FAST_NO_HZ Kconfig option.

Signed-off-by: Paul E. McKenney

torture: Update initrd documentation

2020-08-25T01:45:33+00:00

The rcu-test-image.txt documentation covers a very uncommon case where
a real userspace environment is required.  However, someone reading this
document might reasonably conclude that this is in fact a prerequisite.
In addition, the initrd.txt file mentions dracut, which is no longer used.
This commit therefore provides the needed updates.

Signed-off-by: Paul E. McKenney

rcutorture: Replace HTTP links with HTTPS ones

2020-08-25T01:45:32+00:00

Rationale:
Reduces attack surface on kernel devs opening the links for MITM
as HTTPS traffic is much harder to manipulate.

Deterministic algorithm:
For each file:
  If not .svg:
    For each line:
      If doesn't contain `\bxmlns\b`:
        For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`:
	  If neither `\bgnu\.org/license`, nor `\bmozilla\.org/MPL\b`:
            If both the HTTP and HTTPS versions
            return 200 OK and serve the same content:
              Replace HTTP with HTTPS.

Signed-off-by: Alexander A. Klimov 
Signed-off-by: Paul E. McKenney

rcutorture: Remove CONFIG_HOTPLUG_CPU=n from scenarios

2019-10-05T18:49:13+00:00

A number of mainstream CPU families are no longer capable of building
kernels having CONFIG_SMP=y and CONFIG_HOTPLUG_CPU=n, so this commit
removes this combination from the rcutorture scenarios having it.
People wishing to try out this combination may still do so using the
"--kconfig CONFIG_HOTPLUG_CPU=n CONFIG_SUSPEND=n CONFIG_HIBERNATION=n"
argument to the tools/testing/selftests/rcutorture/bin/kvm.sh script
that is used to run rcutorture.

Signed-off-by: Paul E. McKenney

rcutorture: Add initrd support for systems lacking dracut

2018-11-09T05:52:55+00:00

The support for creating initrd directories using dracut is a great
improvement over having to always hand-create them, it is a bit annoying
to have to install some otherwise irrelevant package just to be able to
run rcutorture.  This commit therefore adds support for creating initrd
directories on systems innocent of dracut.  You do need gcc, but then
again you need that to build the kernel (or to build llvm) in any case.

The idea is to create an initrd directory containing nothing but a
statically linked binary having a for-loop over a long-term sleep().
The result is a Linux kernel with almost no userspace: even the
time-honored /dev, /lib, /tmp, and /usr directories are gone.  In fact,
the only directory present is "/", but only because I don't know how to
get rid of it, at least short of not having an initrd in the first place.
Although statically linked binaries are much maligned, and rightly so,
their disadvantages seem to be irrelevant for this particular use case.
From https://www.akkadia.org/drepper/no_static_linking.html:

1.	Fixes are difficult to apply to hordes of widely scattered
	statically linked binaries.  But in this case, there is only one
	binary, but there would otherwise be no fewer than four libraries.

2.	Security measures like local address randomization cannot be used.
	Prudence prevents me from asserting that it is impossible to
	base a remote attack on a networking-free rcutorture instance.
	Nevertheless, bonus points to the first person who comes up with
	such an attack!

3.	More efficient use of physical memory.  Not in this case, given
	that libc is 1.8MB and the statically linked binary "only" 800K.

4.	Features such as locales, name service switch (NSS),
	internationalized domain names (IDN) tool, and so on require
	dynamic linking.  Bonus points to the first person coming up
	with a valid rcutorture use case requiring these features in
	its initrd.

5.	Accidental violations of (L)GPL.  Actually, this change actually
	helps -avoid- such violations by reducing the temptation to
	pass around tarballs of rcutorture-ready initrd directories.
	After all, the rcutorture scripts automatically create an initrd
	directory for you, so why bother with the tarballs?

6.	Tools and hacks like ltrace, LD_PRELOAD, LD_PROFILE, and LD_AUDIT
	don't work.  Again, bonus points to the first person coming up
	with a valid rcutorture use case requiring these features in
	its initrd.

Nevertheless, the script will use dracut if available, and will create the
statically linked binary only when dracut are missing.  Those preferring
the smaller initrd directory resulting from the statically linked binary
(like me) are free to hand-edit mkinitrd.sh to remove the code using
dracut.  ;-)

Signed-off-by: Paul E. McKenney

doc: Fix typo in rcutorture documentation

2018-02-21T00:10:19+00:00

Signed-off-by: Lihao Liang 
Signed-off-by: Paul E. McKenney

rcu: Drive TASKS_RCU directly off of PREEMPT

2017-08-17T14:26:04+00:00

The actual use of TASKS_RCU is only when PREEMPT, otherwise RCU-sched
is used instead.  This commit therefore makes synchronize_rcu_tasks()
and call_rcu_tasks() available always, but mapped to synchronize_sched()
and call_rcu_sched(), respectively, when !PREEMPT.  This approach also
allows some #ifdefs to be removed from rcutorture.

Reported-by: Ingo Molnar 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Masami Hiramatsu 
Acked-by: Ingo Molnar

rcu: Eliminate NOCBs CPU-state Kconfig options

2017-06-09T01:52:43+00:00

The CONFIG_RCU_NOCB_CPU_ALL, CONFIG_RCU_NOCB_CPU_NONE, and
CONFIG_RCU_NOCB_CPU_ZERO Kconfig options are used only in testing and
are redundant with the rcu_nocbs= boot parameter.  This commit therefore
removes these three Kconfig options and adjusts the rcutorture scripts
to use the boot parameter instead.

Signed-off-by: Paul E. McKenney

rcu: Remove debugfs tracing

2017-06-09T01:52:43+00:00

RCU's debugfs tracing used to be the only reasonable low-level debug
information available, but ftrace and event tracing has since surpassed
the RCU debugfs level of usefulness.  This commit therefore removes
RCU's debugfs tracing.

Signed-off-by: Paul E. McKenney