talos-obmc-linux/kernel/rcu, branch dev-4.13

rcu: Fix up pending cbs check in rcu_prepare_for_idle

2017-11-24T07:35:58+00:00

commit 135bd1a230bb69a68c9808a7d25467318900b80a upstream. The pending-callbacks check in rcu_prepare_for_idle() is backwards. It should accelerate if there are pending callbacks, but the check rather uselessly accelerates only if there are no callbacks. This commit therefore inverts this check. Fixes: 15fecf89e46a ("srcu: Abstract multi-tail callback list handling") Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney Signed-off-by: Greg Kroah-Hartman

rcu: Allow for page faults in NMI handlers

2017-10-05T07:47:31+00:00

commit 28585a832602747cbfa88ad8934013177a3aae38 upstream. A number of architecture invoke rcu_irq_enter() on exception entry in order to allow RCU read-side critical sections in the exception handler when the exception is from an idle or nohz_full CPU. This works, at least unless the exception happens in an NMI handler. In that case, rcu_nmi_enter() would already have exited the extended quiescent state, which would mean that rcu_irq_enter() would (incorrectly) cause RCU to think that it is again in an extended quiescent state. This will in turn result in lockdep splats in response to later RCU read-side critical sections. This commit therefore causes rcu_irq_enter() and rcu_irq_exit() to take no action if there is an rcu_nmi_enter() in effect, thus avoiding the unscheduled return to RCU quiescent state. This in turn should make the kernel safe for on-demand RCU voyeurism. Link: http://lkml.kernel.org/r/20170922211022.GA18084@linux.vnet.ibm.com Fixes: 0be964be0 ("module: Sanitize RCU usage and locking") Reported-by: Steven Rostedt Signed-off-by: Paul E. McKenney Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Greg Kroah-Hartman

srcu: Provide ordering for CPU not involved in grace period

2017-09-27T12:43:11+00:00

commit 35732cf9dd38b1efb0f2f22c91c61b51337d1ac3 upstream. Tree RCU guarantees that every online CPU has a memory barrier between any given grace period and any of that CPU's RCU read-side sections that must be ordered against that grace period. Since RCU doesn't always know where read-side critical sections are, the actual implementation guarantees order against prior and subsequent non-idle non-offline code, whether in an RCU read-side critical section or not. As a result, there does not need to be a memory barrier at the end of synchronize_rcu() and friends because the ordering internal to the grace period has ordered every CPU's post-grace-period execution against each CPU's pre-grace-period execution, again for all non-idle online CPUs. In contrast, SRCU can have non-idle online CPUs that are completely uninvolved in a given SRCU grace period, for example, a CPU that never runs any SRCU read-side critical sections and took no part in the grace-period processing. It is in theory possible for a given synchronize_srcu()'s wakeup to be delivered to a CPU that was completely uninvolved in the prior SRCU grace period, which could mean that the code following that synchronize_srcu() would end up being unordered with respect to both the grace period and any pre-existing SRCU read-side critical sections. This commit therefore adds an smp_mb() to the end of __synchronize_srcu(), which prevents this scenario from occurring. Reported-by: Lance Roy Signed-off-by: Paul E. McKenney Acked-by: Lance Roy Signed-off-by: Greg Kroah-Hartman

rcu: Remove RCU CPU stall warnings from Tiny RCU

2017-06-09T01:52:45+00:00

Tiny RCU's job is to be tiny, so this commit removes its RCU CPU stall warning code. After this, there is no longer any need for rcu_sched_ctrlblk and rcu_bh_ctrlblk to be in tiny_plugin.h, so this commit also moves them to tiny.c. Signed-off-by: Paul E. McKenney

rcu: Remove event tracing from Tiny RCU

2017-06-09T01:52:45+00:00

This commit saves a few lines by getting rid of Tiny RCU's event tracing. Signed-off-by: Paul E. McKenney

rcu: Move RCU debug Kconfig options to kernel/rcu

2017-06-09T01:52:44+00:00

RCU's debugging Kconfig options are in the unintuitive location lib/Kconfig.debug, and there are enough of them that it would be good for them to be more centralized. This commit therefore extracts RCU's Kconfig options from init/Kconfig into a new kernel/rcu/Kconfig.debug file. Reported-by: Ingo Molnar Signed-off-by: Paul E. McKenney

rcu: Move RCU non-debug Kconfig options to kernel/rcu

2017-06-09T01:52:44+00:00

RCU's Kconfig options are scattered, and there are enough of them that it would be good for them to be more centralized. This commit therefore extracts RCU's Kconfig options from init/Kconfig into a new kernel/rcu/Kconfig file. Reported-by: Ingo Molnar Signed-off-by: Paul E. McKenney

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

srcu: Remove Classic SRCU

2017-06-09T01:52:42+00:00

Classic SRCU was only ever intended to be a fallback in case of issues with Tree/Tiny SRCU, and the latter two are doing quite well in testing. This commit therefore removes Classic SRCU. Signed-off-by: Paul E. McKenney