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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
  1. kernel/rcutree.c +1 −0
  2. kernel/rcutree.h +1 −0
  3. kernel/rcutree_plugin.h +11 −3
  4. 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 trace_rcu_utilization("Start context switch");202 trace_rcu_utilization("Start context switch");
203 rcu_sched_qs(cpu);203 rcu_sched_qs(cpu);
204 rcu_preempt_note_context_switch(cpu);
204 trace_rcu_utilization("End context switch");205 trace_rcu_utilization("End context switch");
205}206}
206EXPORT_SYMBOL_GPL(rcu_note_context_switch);207EXPORT_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/* Forward declarations for rcutree_plugin.h */444/* Forward declarations for rcutree_plugin.h */
445static void rcu_bootup_announce(void);445static void rcu_bootup_announce(void);
446long rcu_batches_completed(void);446long rcu_batches_completed(void);
447static void rcu_preempt_note_context_switch(int cpu);
447static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);448static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
448#ifdef CONFIG_HOTPLUG_CPU449#ifdef CONFIG_HOTPLUG_CPU
449static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,450static 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 * Caller must disable preemption.154 * Caller must disable preemption.
155 */155 */
156void rcu_preempt_note_context_switch(void)156static void rcu_preempt_note_context_switch(int cpu)
157{157{
158 struct task_struct *t = current;158 struct task_struct *t = current;
159 unsigned long flags;159 unsigned long flags;
@@ -164,7 +164,7 @@ void rcu_preempt_note_context_switch(void) · 4 unmodified lines
164 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {164 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
165 165
166 /* Possibly blocking in an RCU read-side critical section. */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 rnp = rdp->mynode;168 rnp = rdp->mynode;
169 raw_spin_lock_irqsave(&rnp->lock, flags);169 raw_spin_lock_irqsave(&rnp->lock, flags);
170 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;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 * means that we continue to block the current grace period.228 * means that we continue to block the current grace period.
229 */229 */
230 local_irq_save(flags);230 local_irq_save(flags);
231 rcu_preempt_qs(smp_processor_id());231 rcu_preempt_qs(cpu);
232 local_irq_restore(flags);232 local_irq_restore(flags);
233}233}
234 234
@@ -1001,6 +1001,14 @@ void rcu_force_quiescent_state(void) · 766 unmodified lines
1001}1001}
1002EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);1002EXPORT_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 */
1008static void rcu_preempt_note_context_switch(int cpu)
1009{
1010}
1011
1004/*1012/*
1005 * Because preemptible RCU does not exist, there are never any preempted1013 * Because preemptible RCU does not exist, there are never any preempted
1006 * RCU readers.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#endif2081#endif
2082 2082
2083 /* Here we just switch the register state and the stack. */2083 /* Here we just switch the register state and the stack. */
2084 rcu_switch_from(prev);
2085 switch_to(prev, next, prev);2084 switch_to(prev, next, prev);
2086 2085
2087 barrier();2086 barrier();