user/sven/linux.git/kernel/rcu/tree.c, branch v4.9.99

rcu: Allow for page faults in NMI handlers

2017-10-18T07:35:38Z

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

rcu: Narrow early boot window of illegal synchronous grace periods

2017-01-26T07:24:37Z

commit 52d7e48b86fc108e45a656d8e53e4237993c481d upstream. The current preemptible RCU implementation goes through three phases during bootup. In the first phase, there is only one CPU that is running with preemption disabled, so that a no-op is a synchronous grace period. In the second mid-boot phase, the scheduler is running, but RCU has not yet gotten its kthreads spawned (and, for expedited grace periods, workqueues are not yet running. During this time, any attempt to do a synchronous grace period will hang the system (or complain bitterly, depending). In the third and final phase, RCU is fully operational and everything works normally. This has been OK for some time, but there has recently been some synchronous grace periods showing up during the second mid-boot phase. This code worked "by accident" for awhile, but started failing as soon as expedited RCU grace periods switched over to workqueues in commit 8b355e3bc140 ("rcu: Drive expedited grace periods from workqueue"). Note that the code was buggy even before this commit, as it was subject to failure on real-time systems that forced all expedited grace periods to run as normal grace periods (for example, using the rcu_normal ksysfs parameter). The callchain from the failure case is as follows: early_amd_iommu_init() |-> acpi_put_table(ivrs_base); |-> acpi_tb_put_table(table_desc); |-> acpi_tb_invalidate_table(table_desc); |-> acpi_tb_release_table(...) |-> acpi_os_unmap_memory |-> acpi_os_unmap_iomem |-> acpi_os_map_cleanup |-> synchronize_rcu_expedited The kernel showing this callchain was built with CONFIG_PREEMPT_RCU=y, which caused the code to try using workqueues before they were initialized, which did not go well. This commit therefore reworks RCU to permit synchronous grace periods to proceed during this mid-boot phase. This commit is therefore a fix to a regression introduced in v4.9, and is therefore being put forward post-merge-window in v4.10. This commit sets a flag from the existing rcu_scheduler_starting() function which causes all synchronous grace periods to take the expedited path. The expedited path now checks this flag, using the requesting task to drive the expedited grace period forward during the mid-boot phase. Finally, this flag is updated by a core_initcall() function named rcu_exp_runtime_mode(), which causes the runtime codepaths to be used. Note that this arrangement assumes that tasks are not sent POSIX signals (or anything similar) from the time that the first task is spawned through core_initcall() time. Fixes: 8b355e3bc140 ("rcu: Drive expedited grace periods from workqueue") Reported-by: "Zheng, Lv" Reported-by: Borislav Petkov Signed-off-by: Paul E. McKenney Tested-by: Stan Kain Tested-by: Ivan Tested-by: Emanuel Castelo Tested-by: Bruno Pesavento Tested-by: Borislav Petkov Tested-by: Frederic Bezies Signed-off-by: Greg Kroah-Hartman

Merge tag 'gcc-plugins-v4.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

2016-10-15T17:03:15Z

Pull gcc plugins update from Kees Cook: "This adds a new gcc plugin named "latent_entropy". It is designed to extract as much possible uncertainty from a running system at boot time as possible, hoping to capitalize on any possible variation in CPU operation (due to runtime data differences, hardware differences, SMP ordering, thermal timing variation, cache behavior, etc). At the very least, this plugin is a much more comprehensive example for how to manipulate kernel code using the gcc plugin internals" * tag 'gcc-plugins-v4.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: latent_entropy: Mark functions with __latent_entropy gcc-plugins: Add latent_entropy plugin

latent_entropy: Mark functions with __latent_entropy

2016-10-10T21:51:45Z

The __latent_entropy gcc attribute can be used only on functions and variables. If it is on a function then the plugin will instrument it for gathering control-flow entropy. If the attribute is on a variable then the plugin will initialize it with random contents. The variable must be an integer, an integer array type or a structure with integer fields. These specific functions have been selected because they are init functions (to help gather boot-time entropy), are called at unpredictable times, or they have variable loops, each of which provide some level of latent entropy. Signed-off-by: Emese Revfy [kees: expanded commit message] Signed-off-by: Kees Cook

Merge branches 'doc.2016.08.22c', 'exp.2016.08.22c', 'fixes.2016.09.14a', 'hotplug.2016.08.22c' and 'torture.2016.08.22c' into HEAD

2016-09-14T19:58:49Z

doc.2016.08.22c: Documentation updates exp.2016.08.22c: Expedited grace-period updates fixes.2016.09.14a: Miscellaneous fixes hotplug.2016.08.22c: CPU-hotplug changes torture.2016.08.22c: Torture-test changes

rcu: Provide exact CPU-online tracking for RCU

2016-08-22T16:36:57Z

Up to now, RCU has assumed that the CPU-online process makes it from CPU_UP_PREPARE to set_cpu_online() within one jiffy. Given the recent rise of virtualized environments, this assumption is very clearly obsolete. Failing to meet this deadline can result in RCU paying attention to an incoming CPU for one jiffy, then ignoring it until the grace period following the one in which that CPU sets itself online. This situation might prove to be fatally disappointing to any RCU read-side critical sections that had the misfortune to execute during the time in which RCU was ignoring the slow-to-come-online CPU. This commit therefore updates RCU's internal CPU state-tracking information at notify_cpu_starting() time, thus providing RCU with an exact transition of the CPU's state from offline to online. Note that this means that incoming CPUs must not use RCU read-side critical section (other than those of SRCU) until notify_cpu_starting() time. Note also that the CPU_STARTING notifiers -are- allowed to use RCU read-side critical sections. (Of course, CPU-hotplug notifiers are rapidly becoming obsolete, so you need to act fast!) If a given architecture or CPU family needs to use RCU read-side critical sections earlier, the call to rcu_cpu_starting() from notify_cpu_starting() will need to be architecture-specific, with architectures that need early use being required to hand-place the call to rcu_cpu_starting() at some point preceding the call to notify_cpu_starting(). Signed-off-by: Paul E. McKenney

rcu: Avoid redundant quiescent-state chasing

2016-08-22T16:35:57Z

Currently, __note_gp_changes() checks to see if the CPU has slept through multiple grace periods. If it has, it resynchronizes that CPU's view of the grace-period state, which includes whether or not the current grace period needs a quiescent state from this CPU. The fact of this need (or lack thereof) needs to be in two places, rdp->cpu_no_qs.b.norm and rdp->core_needs_qs. The former tells RCU's context-switch code to go get a quiescent state and the latter says that it needs to be reported. The current code unconditionally sets the former to true, but correctly sets the latter. This does not result in failures, but it does unnecessarily increase the amount of work done on average at context-switch time. This commit therefore correctly sets both fields. Signed-off-by: Paul E. McKenney

rcu: Don't use modular infrastructure in non-modular code

2016-08-22T16:35:27Z

The Kconfig currently controlling compilation of tree.c is: init/Kconfig:config TREE_RCU init/Kconfig: bool ...and update.c and sync.c are "obj-y" meaning that none are ever built as a module by anyone. Since MODULE_ALIAS is a no-op for non-modular code, we can remove them from these files. We leave moduleparam.h behind since the files instantiate some boot time configuration parameters with module_param() still. Cc: "Paul E. McKenney" Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Signed-off-by: Paul Gortmaker Signed-off-by: Paul E. McKenney

rcu: Use rcu_gp_kthread_wake() to wake up grace period kthreads

2016-08-22T16:33:46Z

Commit abedf8e2419f ("rcu: Use simple wait queues where possible in rcutree") converts Tree RCU's wait queues to simple wait queues, but it incorrectly reverts the commit 2aa792e6faf1 ("rcu: Use rcu_gp_kthread_wake() to wake up grace period kthreads"). This can result in redundant self-wakeups. This commit therefore replaces the simple wait-queue wakeups with rcu_gp_kthread_wake(), thus avoiding the redundant wakeups. Signed-off-by: Jisheng Zhang Signed-off-by: Paul E. McKenney

rcu: Convert rcutree to hotplug state machine

2016-07-15T08:41:44Z

Straight forward conversion to the state machine. Though the question arises whether this needs really all these state transitions to work. Signed-off-by: Thomas Gleixner Signed-off-by: Anna-Maria Gleixner Reviewed-by: Sebastian Andrzej Siewior Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: rt@linutronix.de Link: http://lkml.kernel.org/r/20160713153337.982013161@linutronix.de Signed-off-by: Ingo Molnar