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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

Unified · Split

8 files
  1. arch/um/drivers/mconsole_kern.c +0 −1
  2. include/linux/rcupdate.h +0 −1
  3. include/linux/rcutiny.h +6 −0
  4. include/linux/sched.h +0 −10
  5. kernel/rcutree.c +1 −0
  6. kernel/rcutree.h +1 −0
  7. kernel/rcutree_plugin.h +11 −3
  8. kernel/sched/core.c +0 −1
arch/um/drivers/mconsole_kern.c+0−1
@@ -705,7 +705,6 @@ static void stack_proc(void *arg) · 704 unmodified lines
705705 struct task_struct *from = current, *to = arg;
706706
707707 to->thread.saved_task = from;
708− rcu_switch_from(from);
709708 switch_to(from, to, from);
710709 }
711710
include/linux/rcupdate.h+0−1
@@ -184,7 +184,6 @@ static inline int rcu_preempt_depth(void) · 183 unmodified lines
184184 /* Internal to kernel */
185185 extern void rcu_sched_qs(int cpu);
186186 extern void rcu_bh_qs(int cpu);
187−extern void rcu_preempt_note_context_switch(void);
188187 extern void rcu_check_callbacks(int cpu, int user);
189188 struct notifier_block;
190189 extern void rcu_idle_enter(void);
include/linux/rcutiny.h+6−0
@@ -87,6 +87,10 @@ static inline void kfree_call_rcu(struct rcu_head *head, · 86 unmodified lines
8787
8888 #ifdef CONFIG_TINY_RCU
8989
90+static inline void rcu_preempt_note_context_switch(void)
91+{
92+}
93+
9094 static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
9195 {
9296 *delta_jiffies = ULONG_MAX;
@@ -95,6 +99,7 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) · 2 unmodified lines
9599
96100 #else /* #ifdef CONFIG_TINY_RCU */
97101
102+void rcu_preempt_note_context_switch(void);
98103 int rcu_preempt_needs_cpu(void);
99104
100105 static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
@@ -108,6 +113,7 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) · 7 unmodified lines
108113 static inline void rcu_note_context_switch(int cpu)
109114 {
110115 rcu_sched_qs(cpu);
116+ rcu_preempt_note_context_switch();
111117 }
112118
113119 /*
include/linux/sched.h+0−10
@@ -1871,22 +1871,12 @@ static inline void rcu_copy_process(struct task_struct *p) · 1870 unmodified lines
18711871 INIT_LIST_HEAD(&p->rcu_node_entry);
18721872 }
18731873
1874−static inline void rcu_switch_from(struct task_struct *prev)
1875−{
1876− if (prev->rcu_read_lock_nesting != 0)
1877− rcu_preempt_note_context_switch();
1878−}
1879−
18801874 #else
18811875
18821876 static inline void rcu_copy_process(struct task_struct *p)
18831877 {
18841878 }
18851879
1886−static inline void rcu_switch_from(struct task_struct *prev)
1887−{
1888−}
1889−
18901880 #endif
18911881
18921882 #ifdef CONFIG_SMP
kernel/rcutree.c+1−0
@@ -201,6 +201,7 @@ void rcu_note_context_switch(int cpu) · 200 unmodified lines
201201 {
202202 trace_rcu_utilization("Start context switch");
203203 rcu_sched_qs(cpu);
204+ rcu_preempt_note_context_switch(cpu);
204205 trace_rcu_utilization("End context switch");
205206 }
206207 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
444444 /* Forward declarations for rcutree_plugin.h */
445445 static void rcu_bootup_announce(void);
446446 long rcu_batches_completed(void);
447+static void rcu_preempt_note_context_switch(int cpu);
447448 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
448449 #ifdef CONFIG_HOTPLUG_CPU
449450 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
153153 *
154154 * Caller must disable preemption.
155155 */
156−void rcu_preempt_note_context_switch(void)
156+static void rcu_preempt_note_context_switch(int cpu)
157157 {
158158 struct task_struct *t = current;
159159 unsigned long flags;
@@ -164,7 +164,7 @@ void rcu_preempt_note_context_switch(void) · 4 unmodified lines
164164 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
165165
166166 /* 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);
168168 rnp = rdp->mynode;
169169 raw_spin_lock_irqsave(&rnp->lock, flags);
170170 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
@@ -228,7 +228,7 @@ void rcu_preempt_note_context_switch(void) · 57 unmodified lines
228228 * means that we continue to block the current grace period.
229229 */
230230 local_irq_save(flags);
231− rcu_preempt_qs(smp_processor_id());
231+ rcu_preempt_qs(cpu);
232232 local_irq_restore(flags);
233233 }
234234
@@ -1001,6 +1001,14 @@ void rcu_force_quiescent_state(void) · 766 unmodified lines
10011001 }
10021002 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
10031003
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+
10041012 /*
10051013 * Because preemptible RCU does not exist, there are never any preempted
10061014 * RCU readers.
kernel/sched/core.c+0−1
@@ -2081,7 +2081,6 @@ context_switch(struct rq *rq, struct task_struct *prev, · 2080 unmodified lines
20812081 #endif
20822082
20832083 /* Here we just switch the register state and the stack. */
2084− rcu_switch_from(prev);
20852084 switch_to(prev, next, prev);
20862085
20872086 barrier();