rcu: Apply RCU-bh QSes to RCU-sched and RCU-preempt when safe (d28139c4) · Commits · 戴 / test

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. Signed-off-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Fix !SMP issue located by kbuild test robot. ]

include/linux/rcutiny.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -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(); \

include/linux/rcutree.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -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);

kernel/rcu/tree.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -255,6 +255,13 @@ 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.

kernel/rcu/tree.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -433,6 +433,7 @@ 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

kernel/rcu/tree_plugin.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -974,6 +974,11 @@ 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.

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