Revert "rcu: Move PREEMPT_RCU preemption to switch_to() invocation"

This reverts commit 616c310e83b872024271c915c1b9ab505b9efad9. (Move PREEMPT_RCU preemption to switch_to() invocation). Testing by Sasha Levin <levinsasha928@gmail.com> showed that this can result in deadlock due to invoking the scheduler when one of the runqueue locks is held. Because this commit was simply a performance optimization, revert it.

Paul E. McKenney committed 14 years ago

Commit cba6d0d1 parent 6887a418 files · +19 −16Browse files

Showing the changes to kernel (4 of 8 files). Show all

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4 files

kernel/rcutree.c +1 −0
kernel/rcutree.h +1 −0
kernel/rcutree_plugin.h +11 −3
kernel/sched/core.c +0 −1

kernel/rcutree.c+1−0

@@ -201,6 +201,7 @@ void rcu_note_context_switch(int cpu) · 200 unmodified lines
201	201	{
202	202	trace_rcu_utilization("Start context switch");
203	203	rcu_sched_qs(cpu);
	204	+ rcu_preempt_note_context_switch(cpu);
204	205	trace_rcu_utilization("End context switch");
205	206	}
206	207	EXPORT_SYMBOL_GPL(rcu_note_context_switch);

kernel/rcutree.h+1−0

@@ -444,6 +444,7 @@ DECLARE_PER_CPU(char, rcu_cpu_has_work); · 443 unmodified lines
444	444	/* Forward declarations for rcutree_plugin.h */
445	445	static void rcu_bootup_announce(void);
446	446	long rcu_batches_completed(void);
	447	+static void rcu_preempt_note_context_switch(int cpu);
447	448	static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
448	449	#ifdef CONFIG_HOTPLUG_CPU
449	450	static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,

kernel/rcutree_plugin.h+11−3

@@ -153,7 +153,7 @@ static void rcu_preempt_qs(int cpu) · 152 unmodified lines
153	153	*
154	154	* Caller must disable preemption.
155	155	*/
156		−void rcu_preempt_note_context_switch(void)
	156	+static void rcu_preempt_note_context_switch(int cpu)
157	157	{
158	158	struct task_struct *t = current;
159	159	unsigned long flags;
@@ -164,7 +164,7 @@ void rcu_preempt_note_context_switch(void) · 4 unmodified lines
164	164	(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
165	165
166	166	/* Possibly blocking in an RCU read-side critical section. */
167		− rdp = __this_cpu_ptr(rcu_preempt_state.rda);
	167	+ rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
168	168	rnp = rdp->mynode;
169	169	raw_spin_lock_irqsave(&rnp->lock, flags);
170	170	t->rcu_read_unlock_special \|= RCU_READ_UNLOCK_BLOCKED;
@@ -228,7 +228,7 @@ void rcu_preempt_note_context_switch(void) · 57 unmodified lines
228	228	* means that we continue to block the current grace period.
229	229	*/
230	230	local_irq_save(flags);
231		− rcu_preempt_qs(smp_processor_id());
	231	+ rcu_preempt_qs(cpu);
232	232	local_irq_restore(flags);
233	233	}
234	234
@@ -1001,6 +1001,14 @@ void rcu_force_quiescent_state(void) · 766 unmodified lines
1001	1001	}
1002	1002	EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
1003	1003
	1004	+/*
	1005	+ * Because preemptible RCU does not exist, we never have to check for
	1006	+ * CPUs being in quiescent states.
	1007	+ */
	1008	+static void rcu_preempt_note_context_switch(int cpu)
	1009	+{
	1010	+}
	1011	+
1004	1012	/*
1005	1013	* Because preemptible RCU does not exist, there are never any preempted
1006	1014	* RCU readers.

kernel/sched/core.c+0−1

@@ -2081,7 +2081,6 @@ context_switch(struct rq rq, struct task_struct prev, · 2080 unmodified lines
2081	2081	#endif
2082	2082
2083	2083	/* Here we just switch the register state and the stack. */
2084		− rcu_switch_from(prev);
2085	2084	switch_to(prev, next, prev);
2086	2085
2087	2086	barrier();