From c54b096ee0ee03a4d50998ba9069ced4c0bf858a Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 28 Jun 2018 14:45:25 -0700 Subject: [PATCH] UPSTREAM: rcu: Apply RCU-bh QSes to RCU-sched and RCU-preempt when safe One necessary step towards consolidating the three flavors of RCU is to make sure that the resulting consolidated "one flavor to rule them all" correctly handles networking denial-of-service attacks. One thing that allows RCU-bh to do so is that __do_softirq() invokes rcu_bh_qs() every so often, and so something similar has to happen for consolidated RCU. This must be done carefully. For example, if a preemption-disabled region of code takes an interrupt which does softirq processing before returning, consolidated RCU must ignore the resulting rcu_bh_qs() invocations -- preemption is still disabled, and that means an RCU reader for the consolidated flavor. This commit therefore creates a new rcu_softirq_qs() that is called only from the ksoftirqd task, thus avoiding the interrupted-a-preempted-region problem. This new rcu_softirq_qs() function invokes rcu_sched_qs(), rcu_preempt_qs(), and rcu_preempt_deferred_qs(). The latter call handles any deferred quiescent states. Note that __do_softirq() still invokes rcu_bh_qs(). It will continue to do so until a later stage of cleanup when the RCU-bh flavor is removed. Change-Id: Id4e2d284f3f268aa7acf0f8a8b6e9f8d890785c0 Signed-off-by: Paul E. McKenney [ paulmck: Fix !SMP issue located by kbuild test robot. ] --- include/linux/rcutiny.h | 5 +++++ include/linux/rcutree.h | 1 + kernel/rcu/tree.c | 7 +++++++ kernel/rcu/tree.h | 1 + kernel/rcu/tree_plugin.h | 5 +++++ kernel/softirq.c | 2 ++ 6 files changed, 21 insertions(+) diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 01b101e4dc39..7980be8e0080 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -90,6 +90,11 @@ static inline void kfree_call_rcu(struct rcu_head *head, call_rcu(head, func); } +static inline void rcu_softirq_qs(void) +{ + rcu_sched_qs(); +} + #define rcu_note_context_switch(preempt) \ do { \ rcu_sched_qs(); \ diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 37d6fd3b7ff8..2c44a87c328d 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -30,6 +30,7 @@ #ifndef __LINUX_RCUTREE_H #define __LINUX_RCUTREE_H +void rcu_softirq_qs(void); void rcu_note_context_switch(bool preempt); int rcu_needs_cpu(u64 basem, u64 *nextevt); void rcu_cpu_stall_reset(void); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 8f341c566a86..5a28ff21b3c5 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -254,6 +254,13 @@ void rcu_bh_qs(void) } } +void rcu_softirq_qs(void) +{ + rcu_sched_qs(); + rcu_preempt_qs(); + rcu_preempt_deferred_qs(current); +} + /* * Steal a bit from the bottom of ->dynticks for idle entry/exit * control. Initially this is for TLB flushing. diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 0705723a03a9..f25b2e52ae08 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -448,6 +448,7 @@ DECLARE_PER_CPU(char, rcu_cpu_has_work); /* Forward declarations for rcutree_plugin.h */ static void rcu_bootup_announce(void); +static void rcu_preempt_qs(void); static void rcu_preempt_note_context_switch(bool preempt); static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp); #ifdef CONFIG_HOTPLUG_CPU diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index c525d134bbd8..cc1c4fcfbd0a 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -882,6 +882,11 @@ static void __init rcu_bootup_announce(void) rcu_bootup_announce_oddness(); } +/* Because preemptible RCU does not exist, we can ignore its QSes. */ +static void rcu_preempt_qs(void) +{ +} + /* * Because preemptible RCU does not exist, we never have to check for * CPUs being in quiescent states. diff --git a/kernel/softirq.c b/kernel/softirq.c index d48995a6da29..cf5ee5146221 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -310,6 +310,8 @@ restart: __this_cpu_write(active_softirqs, 0); rcu_bh_qs(); + if (__this_cpu_read(ksoftirqd) == current) + rcu_softirq_qs(); local_irq_disable(); pending = local_softirq_pending();