linux/kernel/rcu/tree.c, branch v4.9

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

rcu: Correctly handle sparse possible cpus

2016-06-15T23:00:05Z

In many cases in the RCU tree code, we iterate over the set of cpus for a leaf node described by rcu_node::grplo and rcu_node::grphi, checking per-cpu data for each cpu in this range. However, if the set of possible cpus is sparse, some cpus described in this range are not possible, and thus no per-cpu region will have been allocated (or initialised) for them by the generic percpu code. Erroneous accesses to a per-cpu area for these !possible cpus may fault or may hit other data depending on the addressed generated when the erroneous per cpu offset is applied. In practice, both cases have been observed on arm64 hardware (the former being silent, but detectable with additional patches). To avoid issues resulting from this, we must iterate over the set of *possible* cpus for a given leaf node. This patch add a new helper, for_each_leaf_node_possible_cpu, to enable this. As iteration is often intertwined with rcu_node local bitmask manipulation, a new leaf_node_cpu_bit helper is added to make this simpler and more consistent. The RCU tree code is made to use both of these where appropriate. Without this patch, running reboot at a shell can result in an oops like: [ 3369.075979] Unable to handle kernel paging request at virtual address ffffff8008b21b4c [ 3369.083881] pgd = ffffffc3ecdda000 [ 3369.087270] [ffffff8008b21b4c] *pgd=00000083eca48003, *pud=00000083eca48003, *pmd=0000000000000000 [ 3369.096222] Internal error: Oops: 96000007 [#1] PREEMPT SMP [ 3369.101781] Modules linked in: [ 3369.104825] CPU: 2 PID: 1817 Comm: NetworkManager Tainted: G W 4.6.0+ #3 [ 3369.121239] task: ffffffc0fa13e000 ti: ffffffc3eb940000 task.ti: ffffffc3eb940000 [ 3369.128708] PC is at sync_rcu_exp_select_cpus+0x188/0x510 [ 3369.134094] LR is at sync_rcu_exp_select_cpus+0x104/0x510 [ 3369.139479] pc : [] lr : [] pstate: 200001c5 [ 3369.146860] sp : ffffffc3eb9435a0 [ 3369.150162] x29: ffffffc3eb9435a0 x28: ffffff8008be4f88 [ 3369.155465] x27: ffffff8008b66c80 x26: ffffffc3eceb2600 [ 3369.160767] x25: 0000000000000001 x24: ffffff8008be4f88 [ 3369.166070] x23: ffffff8008b51c3c x22: ffffff8008b66c80 [ 3369.171371] x21: 0000000000000001 x20: ffffff8008b21b40 [ 3369.176673] x19: ffffff8008b66c80 x18: 0000000000000000 [ 3369.181975] x17: 0000007fa951a010 x16: ffffff80086a30f0 [ 3369.187278] x15: 0000007fa9505590 x14: 0000000000000000 [ 3369.192580] x13: ffffff8008b51000 x12: ffffffc3eb940000 [ 3369.197882] x11: 0000000000000006 x10: ffffff8008b51b78 [ 3369.203184] x9 : 0000000000000001 x8 : ffffff8008be4000 [ 3369.208486] x7 : ffffff8008b21b40 x6 : 0000000000001003 [ 3369.213788] x5 : 0000000000000000 x4 : ffffff8008b27280 [ 3369.219090] x3 : ffffff8008b21b4c x2 : 0000000000000001 [ 3369.224406] x1 : 0000000000000001 x0 : 0000000000000140 ... [ 3369.972257] [] sync_rcu_exp_select_cpus+0x188/0x510 [ 3369.978685] [] synchronize_rcu_expedited+0x64/0xa8 [ 3369.985026] [] synchronize_net+0x24/0x30 [ 3369.990499] [] dev_deactivate_many+0x28c/0x298 [ 3369.996493] [] __dev_close_many+0x60/0xd0 [ 3370.002052] [] __dev_close+0x28/0x40 [ 3370.007178] [] __dev_change_flags+0x8c/0x158 [ 3370.012999] [] dev_change_flags+0x20/0x60 [ 3370.018558] [] do_setlink+0x288/0x918 [ 3370.023771] [] rtnl_newlink+0x398/0x6a8 [ 3370.029158] [] rtnetlink_rcv_msg+0xe4/0x220 [ 3370.034891] [] netlink_rcv_skb+0xc4/0xf8 [ 3370.040364] [] rtnetlink_rcv+0x2c/0x40 [ 3370.045663] [] netlink_unicast+0x160/0x238 [ 3370.051309] [] netlink_sendmsg+0x2f0/0x358 [ 3370.056956] [] sock_sendmsg+0x18/0x30 [ 3370.062168] [] ___sys_sendmsg+0x26c/0x280 [ 3370.067728] [] __sys_sendmsg+0x44/0x88 [ 3370.073027] [] SyS_sendmsg+0x10/0x20 [ 3370.078153] [] el0_svc_naked+0x24/0x28 Signed-off-by: Mark Rutland Reported-by: Dennis Chen Cc: Catalin Marinas Cc: Josh Triplett Cc: Lai Jiangshan Cc: Mathieu Desnoyers Cc: Steve Capper Cc: Steven Rostedt Cc: Will Deacon Cc: linux-kernel@vger.kernel.org Signed-off-by: Paul E. McKenney

rcu: sysctl: Panic on RCU Stall

2016-06-15T23:00:05Z

It is not always easy to determine the cause of an RCU stall just by analysing the RCU stall messages, mainly when the problem is caused by the indirect starvation of rcu threads. For example, when preempt_rcu is not awakened due to the starvation of a timer softirq. We have been hard coding panic() in the RCU stall functions for some time while testing the kernel-rt. But this is not possible in some scenarios, like when supporting customers. This patch implements the sysctl kernel.panic_on_rcu_stall. If set to 1, the system will panic() when an RCU stall takes place, enabling the capture of a vmcore. The vmcore provides a way to analyze all kernel/tasks states, helping out to point to the culprit and the solution for the stall. The kernel.panic_on_rcu_stall sysctl is disabled by default. Changes from v1: - Fixed a typo in the git log - The if(sysctl_panic_on_rcu_stall) panic() is in a static function - Fixed the CONFIG_TINY_RCU compilation issue - The var sysctl_panic_on_rcu_stall is now __read_mostly Cc: Jonathan Corbet Cc: "Paul E. McKenney" Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Acked-by: Christian Borntraeger Reviewed-by: Josh Triplett Reviewed-by: Arnaldo Carvalho de Melo Tested-by: "Luis Claudio R. Goncalves" Signed-off-by: Daniel Bristot de Oliveira Signed-off-by: Paul E. McKenney