perf_counter: Clean up task_ctx vs interrupts

Remove the local_irq_save() etc.. in routines that are smp function
calls, or have IRQs disabled by other means.

Then change the COMM, MMAP, and swcounter context iteration to
current->perf_counter_ctxp and RCU, since it really doesn't matter
which context they iterate, they're all folded.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/perf_counter.c

@@ -232,18 +232,14 @@ static void __perf_counter_remove_from_context(void *info)
 	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
 	struct perf_counter *counter = info;
 	struct perf_counter_context *ctx = counter->ctx;
-	unsigned long flags;
 
-	local_irq_save(flags);
 	/*
 	 * If this is a task context, we need to check whether it is
 	 * the current task context of this cpu. If not it has been
 	 * scheduled out before the smp call arrived.
 	 */
-	if (ctx->task && cpuctx->task_ctx != ctx) {
-		local_irq_restore(flags);
+	if (ctx->task && cpuctx->task_ctx != ctx)
 		return;
-	}
 
 	spin_lock(&ctx->lock);
 	/*
@@ -267,7 +263,7 @@ static void __perf_counter_remove_from_context(void *info)
 	}
 
 	perf_enable();
-	spin_unlock_irqrestore(&ctx->lock, flags);
+	spin_unlock(&ctx->lock);
 }
 
 
@@ -383,17 +379,13 @@ static void __perf_counter_disable(void *info)
 	struct perf_counter *counter = info;
 	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
 	struct perf_counter_context *ctx = counter->ctx;
-	unsigned long flags;
 
-	local_irq_save(flags);
 	/*
 	 * If this is a per-task counter, need to check whether this
 	 * counter's task is the current task on this cpu.
 	 */
-	if (ctx->task && cpuctx->task_ctx != ctx) {
-		local_irq_restore(flags);
+	if (ctx->task && cpuctx->task_ctx != ctx)
 		return;
-	}
 
 	spin_lock(&ctx->lock);
 
@@ -411,7 +403,7 @@ static void __perf_counter_disable(void *info)
 		counter->state = PERF_COUNTER_STATE_OFF;
 	}
 
-	spin_unlock_irqrestore(&ctx->lock, flags);
+	spin_unlock(&ctx->lock);
 }
 
 /*
@@ -618,10 +610,8 @@ static void __perf_install_in_context(void *info)
 	struct perf_counter_context *ctx = counter->ctx;
 	struct perf_counter *leader = counter->group_leader;
 	int cpu = smp_processor_id();
-	unsigned long flags;
 	int err;
 
-	local_irq_save(flags);
 	/*
 	 * If this is a task context, we need to check whether it is
 	 * the current task context of this cpu. If not it has been
@@ -630,10 +620,8 @@ static void __perf_install_in_context(void *info)
 	 * on this cpu because it had no counters.
 	 */
 	if (ctx->task && cpuctx->task_ctx != ctx) {
-		if (cpuctx->task_ctx || ctx->task != current) {
-			local_irq_restore(flags);
+		if (cpuctx->task_ctx || ctx->task != current)
 			return;
-		}
 		cpuctx->task_ctx = ctx;
 	}
 
@@ -687,7 +675,7 @@ static void __perf_install_in_context(void *info)
  unlock:
 	perf_enable();
 
-	spin_unlock_irqrestore(&ctx->lock, flags);
+	spin_unlock(&ctx->lock);
 }
 
 /*
@@ -751,19 +739,15 @@ static void __perf_counter_enable(void *info)
 	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
 	struct perf_counter_context *ctx = counter->ctx;
 	struct perf_counter *leader = counter->group_leader;
-	unsigned long flags;
 	int err;
 
-	local_irq_save(flags);
 	/*
 	 * If this is a per-task counter, need to check whether this
 	 * counter's task is the current task on this cpu.
 	 */
 	if (ctx->task && cpuctx->task_ctx != ctx) {
-		if (cpuctx->task_ctx || ctx->task != current) {
-			local_irq_restore(flags);
+		if (cpuctx->task_ctx || ctx->task != current)
 			return;
-		}
 		cpuctx->task_ctx = ctx;
 	}
 
@@ -811,7 +795,7 @@ static void __perf_counter_enable(void *info)
 	}
 
  unlock:
-	spin_unlock_irqrestore(&ctx->lock, flags);
+	spin_unlock(&ctx->lock);
 }
 
 /*
@@ -981,6 +965,10 @@ void perf_counter_task_sched_out(struct task_struct *task,
 		spin_lock(&ctx->lock);
 		spin_lock_nested(&next_ctx->lock, SINGLE_DEPTH_NESTING);
 		if (context_equiv(ctx, next_ctx)) {
+			/*
+			 * XXX do we need a memory barrier of sorts
+			 * wrt to rcu_dereference() of perf_counter_ctxp
+			 */
 			task->perf_counter_ctxp = next_ctx;
 			next->perf_counter_ctxp = ctx;
 			ctx->task = next;
@@ -998,6 +986,9 @@ void perf_counter_task_sched_out(struct task_struct *task,
 	}
 }
 
+/*
+ * Called with IRQs disabled
+ */
 static void __perf_counter_task_sched_out(struct perf_counter_context *ctx)
 {
 	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
@@ -1012,6 +1003,9 @@ static void __perf_counter_task_sched_out(struct perf_counter_context *ctx)
 	cpuctx->task_ctx = NULL;
 }
 
+/*
+ * Called with IRQs disabled
+ */
 static void perf_counter_cpu_sched_out(struct perf_cpu_context *cpuctx)
 {
 	__perf_counter_sched_out(&cpuctx->ctx, cpuctx);
@@ -2431,6 +2425,7 @@ static void perf_counter_comm_ctx(struct perf_counter_context *ctx,
 static void perf_counter_comm_event(struct perf_comm_event *comm_event)
 {
 	struct perf_cpu_context *cpuctx;
+	struct perf_counter_context *ctx;
 	unsigned int size;
 	char *comm = comm_event->task->comm;
 
@@ -2443,9 +2438,17 @@ static void perf_counter_comm_event(struct perf_comm_event *comm_event)
 
 	cpuctx = &get_cpu_var(perf_cpu_context);
 	perf_counter_comm_ctx(&cpuctx->ctx, comm_event);
-	if (cpuctx->task_ctx)
-		perf_counter_comm_ctx(cpuctx->task_ctx, comm_event);
 	put_cpu_var(perf_cpu_context);
+
+	rcu_read_lock();
+	/*
+	 * doesn't really matter which of the child contexts the
+	 * events ends up in.
+	 */
+	ctx = rcu_dereference(current->perf_counter_ctxp);
+	if (ctx)
+		perf_counter_comm_ctx(ctx, comm_event);
+	rcu_read_unlock();
 }
 
 void perf_counter_comm(struct task_struct *task)
@@ -2536,6 +2539,7 @@ static void perf_counter_mmap_ctx(struct perf_counter_context *ctx,
 static void perf_counter_mmap_event(struct perf_mmap_event *mmap_event)
 {
 	struct perf_cpu_context *cpuctx;
+	struct perf_counter_context *ctx;
 	struct file *file = mmap_event->file;
 	unsigned int size;
 	char tmp[16];
@@ -2568,10 +2572,18 @@ got_name:
 
 	cpuctx = &get_cpu_var(perf_cpu_context);
 	perf_counter_mmap_ctx(&cpuctx->ctx, mmap_event);
-	if (cpuctx->task_ctx)
-		perf_counter_mmap_ctx(cpuctx->task_ctx, mmap_event);
 	put_cpu_var(perf_cpu_context);
 
+	rcu_read_lock();
+	/*
+	 * doesn't really matter which of the child contexts the
+	 * events ends up in.
+	 */
+	ctx = rcu_dereference(current->perf_counter_ctxp);
+	if (ctx)
+		perf_counter_mmap_ctx(ctx, mmap_event);
+	rcu_read_unlock();
+
 	kfree(buf);
 }
 
@@ -2882,6 +2894,7 @@ static void __perf_swcounter_event(enum perf_event_types type, u32 event,
 {
 	struct perf_cpu_context *cpuctx = &get_cpu_var(perf_cpu_context);
 	int *recursion = perf_swcounter_recursion_context(cpuctx);
+	struct perf_counter_context *ctx;
 
 	if (*recursion)
 		goto out;
@@ -2891,10 +2904,15 @@ static void __perf_swcounter_event(enum perf_event_types type, u32 event,
 
 	perf_swcounter_ctx_event(&cpuctx->ctx, type, event,
 				 nr, nmi, regs, addr);
-	if (cpuctx->task_ctx) {
-		perf_swcounter_ctx_event(cpuctx->task_ctx, type, event,
-					 nr, nmi, regs, addr);
-	}
+	rcu_read_lock();
+	/*
+	 * doesn't really matter which of the child contexts the
+	 * events ends up in.
+	 */
+	ctx = rcu_dereference(current->perf_counter_ctxp);
+	if (ctx)
+		perf_swcounter_ctx_event(ctx, type, event, nr, nmi, regs, addr);
+	rcu_read_unlock();
 
 	barrier();
 	(*recursion)--;