user/sven/linux.git/include/linux/rcupdate.h, branch v4.9.109

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

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

Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next

2016-07-27T19:03:20Z

Pull networking updates from David Miller: 1) Unified UDP encapsulation offload methods for drivers, from Alexander Duyck. 2) Make DSA binding more sane, from Andrew Lunn. 3) Support QCA9888 chips in ath10k, from Anilkumar Kolli. 4) Several workqueue usage cleanups, from Bhaktipriya Shridhar. 5) Add XDP (eXpress Data Path), essentially running BPF programs on RX packets as soon as the device sees them, with the option to mirror the packet on TX via the same interface. From Brenden Blanco and others. 6) Allow qdisc/class stats dumps to run lockless, from Eric Dumazet. 7) Add VLAN support to b53 and bcm_sf2, from Florian Fainelli. 8) Simplify netlink conntrack entry layout, from Florian Westphal. 9) Add ipv4 forwarding support to mlxsw spectrum driver, from Ido Schimmel, Yotam Gigi, and Jiri Pirko. 10) Add SKB array infrastructure and convert tun and macvtap over to it. From Michael S Tsirkin and Jason Wang. 11) Support qdisc packet injection in pktgen, from John Fastabend. 12) Add neighbour monitoring framework to TIPC, from Jon Paul Maloy. 13) Add NV congestion control support to TCP, from Lawrence Brakmo. 14) Add GSO support to SCTP, from Marcelo Ricardo Leitner. 15) Allow GRO and RPS to function on macsec devices, from Paolo Abeni. 16) Support MPLS over IPV4, from Simon Horman. * git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next: (1622 commits) xgene: Fix build warning with ACPI disabled. be2net: perform temperature query in adapter regardless of its interface state l2tp: Correctly return -EBADF from pppol2tp_getname. net/mlx5_core/health: Remove deprecated create_singlethread_workqueue net: ipmr/ip6mr: update lastuse on entry change macsec: ensure rx_sa is set when validation is disabled tipc: dump monitor attributes tipc: add a function to get the bearer name tipc: get monitor threshold for the cluster tipc: make cluster size threshold for monitoring configurable tipc: introduce constants for tipc address validation net: neigh: disallow transition to NUD_STALE if lladdr is unchanged in neigh_update() MAINTAINERS: xgene: Add driver and documentation path Documentation: dtb: xgene: Add MDIO node dtb: xgene: Add MDIO node drivers: net: xgene: ethtool: Use phy_ethtool_gset and sset drivers: net: xgene: Use exported functions drivers: net: xgene: Enable MDIO driver drivers: net: xgene: Add backward compatibility drivers: net: phy: xgene: Add MDIO driver ...

rcu: Suppress sparse warnings for rcu_dereference_raw()

2016-07-06T09:51:14Z

Data structures that are used both with and without RCU protection are difficult to write in a sparse-clean manner. If you mark the relevant pointers with __rcu, sparse will complain about all non-RCU uses, but if you don't mark those pointers, sparse will complain about all RCU uses. This commit therefore suppresses sparse warnings for rcu_dereference_raw(), allowing mixed-protection data structures to avoid these warnings. Reported-by: David Howells Signed-off-by: Paul E. McKenney Signed-off-by: David Howells

rcu: Make call_rcu_tasks() tolerate first call with irqs disabled

2016-06-15T22:45:00Z

Currently, if the very first call to call_rcu_tasks() has irqs disabled, it will create the rcu_tasks_kthread with irqs disabled, which will result in a splat in the memory allocator, which kthread_run() invokes with the expectation that irqs are enabled. This commit fixes this problem by deferring kthread creation if called with irqs disabled. The first call to call_rcu_tasks() that has irqs enabled will create the kthread. This bug was detected by rcutorture changes that were motivated by Iftekhar Ahmed's mutation-testing efforts. Signed-off-by: Paul E. McKenney

rcu: No ordering for rcu_assign_pointer() of NULL

2016-06-15T22:31:28Z

This commit does a compile-time check for rcu_assign_pointer() of NULL, and uses WRITE_ONCE() rather than smp_store_release() in that case. Reported-by: Christoph Hellwig Signed-off-by: Paul E. McKenney

rcu: Document RCU_NONIDLE() restrictions in comment header

2016-06-14T23:01:42Z

Signed-off-by: Paul E. McKenney

rcu: Remove superfluous versions of rcu_read_lock_sched_held()

2016-03-31T20:34:50Z

Currently, we have four versions of rcu_read_lock_sched_held(), depending on the combined choices on PREEMPT_COUNT and DEBUG_LOCK_ALLOC. However, there is an existing function preemptible() that already distinguishes between the PREEMPT_COUNT=y and PREEMPT_COUNT=n cases, and allows these four implementations to be consolidated down to two. This commit therefore uses preemptible() to achieve this consolidation. Note that there could be a small performance regression in the case of CONFIG_DEBUG_LOCK_ALLOC=y && PREEMPT_COUNT=n. However, given the overhead associated with CONFIG_DEBUG_LOCK_ALLOC=y, this should be down in the noise. Signed-off-by: Boqun Feng Signed-off-by: Paul E. McKenney

rcu: Consolidate dumping of ftrace buffer

2016-03-31T20:29:08Z

This commit consolidates a couple definitions and several calls for single-shot ftrace-buffer dumping. Signed-off-by: Paul E. McKenney

Merge branch 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2016-03-15T20:50:29Z

Pull cpu hotplug updates from Thomas Gleixner: "This is the first part of the ongoing cpu hotplug rework: - Initial implementation of the state machine - Runs all online and prepare down callbacks on the plugged cpu and not on some random processor - Replaces busy loop waiting with completions - Adds tracepoints so the states can be followed" More detailed commentary on this work from an earlier email: "What's wrong with the current cpu hotplug infrastructure? - Asymmetry The hotplug notifier mechanism is asymmetric versus the bringup and teardown. This is mostly caused by the notifier mechanism. - Largely undocumented dependencies While some notifiers use explicitely defined notifier priorities, we have quite some notifiers which use numerical priorities to express dependencies without any documentation why. - Control processor driven Most of the bringup/teardown of a cpu is driven by a control processor. While it is understandable, that preperatory steps, like idle thread creation, memory allocation for and initialization of essential facilities needs to be done before a cpu can boot, there is no reason why everything else must run on a control processor. Before this patch series, bringup looks like this: Control CPU Booting CPU do preparatory steps kick cpu into life do low level init sync with booting cpu sync with control cpu bring the rest up - All or nothing approach There is no way to do partial bringups. That's something which is really desired because we waste e.g. at boot substantial amount of time just busy waiting that the cpu comes to life. That's stupid as we could very well do preparatory steps and the initial IPI for other cpus and then go back and do the necessary low level synchronization with the freshly booted cpu. - Minimal debuggability Due to the notifier based design, it's impossible to switch between two stages of the bringup/teardown back and forth in order to test the correctness. So in many hotplug notifiers the cancel mechanisms are either not existant or completely untested. - Notifier [un]registering is tedious To [un]register notifiers we need to protect against hotplug at every callsite. There is no mechanism that bringup/teardown callbacks are issued on the online cpus, so every caller needs to do it itself. That also includes error rollback. What's the new design? The base of the new design is a symmetric state machine, where both the control processor and the booting/dying cpu execute a well defined set of states. Each state is symmetric in the end, except for some well defined exceptions, and the bringup/teardown can be stopped and reversed at almost all states. So the bringup of a cpu will look like this in the future: Control CPU Booting CPU do preparatory steps kick cpu into life do low level init sync with booting cpu sync with control cpu bring itself up The synchronization step does not require the control cpu to wait. That mechanism can be done asynchronously via a worker or some other mechanism. The teardown can be made very similar, so that the dying cpu cleans up and brings itself down. Cleanups which need to be done after the cpu is gone, can be scheduled asynchronously as well. There is a long way to this, as we need to refactor the notion when a cpu is available. Today we set the cpu online right after it comes out of the low level bringup, which is not really correct. The proper mechanism is to set it to available, i.e. cpu local threads, like softirqd, hotplug thread etc. can be scheduled on that cpu, and once it finished all booting steps, it's set to online, so general workloads can be scheduled on it. The reverse happens on teardown. First thing to do is to forbid scheduling of general workloads, then teardown all the per cpu resources and finally shut it off completely. This patch series implements the basic infrastructure for this at the core level. This includes the following: - Basic state machine implementation with well defined states, so ordering and prioritization can be expressed. - Interfaces to [un]register state callbacks This invokes the bringup/teardown callback on all online cpus with the proper protection in place and [un]installs the callbacks in the state machine array. For callbacks which have no particular ordering requirement we have a dynamic state space, so that drivers don't have to register an explicit hotplug state. If a callback fails, the code automatically does a rollback to the previous state. - Sysfs interface to drive the state machine to a particular step. This is only partially functional today. Full functionality and therefor testability will be achieved once we converted all existing hotplug notifiers over to the new scheme. - Run all CPU_ONLINE/DOWN_PREPARE notifiers on the booting/dying processor: Control CPU Booting CPU do preparatory steps kick cpu into life do low level init sync with booting cpu sync with control cpu wait for boot bring itself up Signal completion to control cpu In a previous step of this work we've done a full tree mechanical conversion of all hotplug notifiers to the new scheme. The balance is a net removal of about 4000 lines of code. This is not included in this series, as we decided to take a different approach. Instead of mechanically converting everything over, we will do a proper overhaul of the usage sites one by one so they nicely fit into the symmetric callback scheme. I decided to do that after I looked at the ugliness of some of the converted sites and figured out that their hotplug mechanism is completely buggered anyway. So there is no point to do a mechanical conversion first as we need to go through the usage sites one by one again in order to achieve a full symmetric and testable behaviour" * 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (23 commits) cpu/hotplug: Document states better cpu/hotplug: Fix smpboot thread ordering cpu/hotplug: Remove redundant state check cpu/hotplug: Plug death reporting race rcu: Make CPU_DYING_IDLE an explicit call cpu/hotplug: Make wait for dead cpu completion based cpu/hotplug: Let upcoming cpu bring itself fully up arch/hotplug: Call into idle with a proper state cpu/hotplug: Move online calls to hotplugged cpu cpu/hotplug: Create hotplug threads cpu/hotplug: Split out the state walk into functions cpu/hotplug: Unpark smpboot threads from the state machine cpu/hotplug: Move scheduler cpu_online notifier to hotplug core cpu/hotplug: Implement setup/removal interface cpu/hotplug: Make target state writeable cpu/hotplug: Add sysfs state interface cpu/hotplug: Hand in target state to _cpu_up/down cpu/hotplug: Convert the hotplugged cpu work to a state machine cpu/hotplug: Convert to a state machine for the control processor cpu/hotplug: Add tracepoints ...