kernel/tools/testing/selftests/rcutorture/doc, branch linux-5.2.y

rcutorture: Add initrd support for systems lacking dracut

2018-11-09T05:52:55Z

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

2018-02-21T00:10:19Z

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

rcu: Drive TASKS_RCU directly off of PREEMPT

2017-08-17T14:26:04Z

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

2017-06-09T01:52:43Z

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

2017-06-09T01:52:43Z

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

rcu: Remove SPARSE_RCU_POINTER Kconfig option

2017-06-09T01:52:41Z

The sparse-based checking for non-RCU accesses to RCU-protected pointers has been around for a very long time, and it is now the only type of sparse-based checking that is optional. This commit therefore makes it unconditional. Reported-by: Ingo Molnar Signed-off-by: Paul E. McKenney Cc: Fengguang Wu

rcu: Remove the now-obsolete PROVE_RCU_REPEATEDLY Kconfig option

2017-06-09T01:52:41Z

The PROVE_RCU_REPEATEDLY Kconfig option was initially added due to the volume of messages from PROVE_RCU: Doing just one per boot would have required excessive numbers of boots to locate them all. However, PROVE_RCU messages are now relatively rare, so there is no longer any reason to need more than one such message per boot. This commit therefore removes the PROVE_RCU_REPEATEDLY Kconfig option. Signed-off-by: Paul E. McKenney Cc: Ingo Molnar

rcu: Remove nohz_full full-system-idle state machine

2017-06-09T01:52:39Z

The NO_HZ_FULL_SYSIDLE full-system-idle capability was added in 2013 by commit 0edd1b1784cb ("nohz_full: Add full-system-idle state machine"), but has not been used. This commit therefore removes it. If it turns out to be needed later, this commit can always be reverted. Signed-off-by: Paul E. McKenney Cc: Frederic Weisbecker Cc: Rik van Riel Cc: Ingo Molnar Acked-by: Linus Torvalds

rcu: Remove the RCU_KTHREAD_PRIO Kconfig option

2017-06-09T01:52:39Z

Anything that can be done with the RCU_KTHREAD_PRIO Kconfig option can also be done with the rcutree.kthread_prio kernel boot parameter. This commit therefore removes this Kconfig option. Reported-by: Linus Torvalds Signed-off-by: Paul E. McKenney Cc: Frederic Weisbecker Cc: Rik van Riel

rcu: Remove _SLOW_ Kconfig options

2017-06-09T01:52:38Z

The RCU_TORTURE_TEST_SLOW_PREINIT, RCU_TORTURE_TEST_SLOW_PREINIT_DELAY, RCU_TORTURE_TEST_SLOW_PREINIT_DELAY, RCU_TORTURE_TEST_SLOW_INIT, RCU_TORTURE_TEST_SLOW_INIT_DELAY, RCU_TORTURE_TEST_SLOW_CLEANUP, and RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY Kconfig options are only useful for torture testing, and there are the rcutree.gp_cleanup_delay, rcutree.gp_init_delay, and rcutree.gp_preinit_delay kernel boot parameters that rcutorture can use instead. The effect of these parameters is to artificially slow down grace period initialization and cleanup in order to make some types of race conditions happen more often. This commit therefore simplifies Tree RCU a bit by removing the Kconfig options and adding the corresponding kernel parameters to rcutorture's .boot files instead. However, this commit also leaves out the kernel parameters for TREE02, TREE04, and TREE07 in order to have about the same number of tests slowed as not slowed. TREE01, TREE03, TREE05, and TREE06 are slowed, and the rest are not slowed. Reported-by: Linus Torvalds Signed-off-by: Paul E. McKenney

kernel/tools/testing/selftests/rcutorture/doc, branch linux-5.2.y

rcutorture: Add initrd support for systems lacking dracut

doc: Fix typo in rcutorture documentation

rcu: Drive TASKS_RCU directly off of PREEMPT

rcu: Eliminate NOCBs CPU-state Kconfig options

rcu: Remove debugfs tracing

rcu: Remove SPARSE_RCU_POINTER Kconfig option

rcu: Remove the now-obsolete PROVE_RCU_REPEATEDLY Kconfig option

rcu: Remove nohz_full full-system-idle state machine

rcu: Remove the RCU_KTHREAD_PRIO Kconfig option

rcu: Remove *_SLOW_* Kconfig options

rcu: Remove _SLOW_ Kconfig options