perf_events: Undo some recursion damage

Make perf_swevent_get_recursion_context return a context number
and disable preemption.

This could be used to remove the IRQ disable from the trace bit
and index the per-cpu buffer with.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20091123103819.993226816@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 32 insertions, 39 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 50f11b5f8c3..0b0d5f72fe7 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3869,45 +3869,50 @@ static void perf_swevent_ctx_event(struct perf_event_context *ctx,
 	}
 }
 
-/*
- * Must be called with preemption disabled
- */
-int perf_swevent_get_recursion_context(int **recursion)
+int perf_swevent_get_recursion_context(void)
 {
-	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
+	struct perf_cpu_context *cpuctx = &get_cpu_var(perf_cpu_context);
+	int rctx;
 
 	if (in_nmi())
-		*recursion = &cpuctx->recursion[3];
+		rctx = 3;
 	else if (in_irq())
-		*recursion = &cpuctx->recursion[2];
+		rctx = 2;
 	else if (in_softirq())
-		*recursion = &cpuctx->recursion[1];
+		rctx = 1;
 	else
-		*recursion = &cpuctx->recursion[0];
+		rctx = 0;
 
-	if (**recursion)
+	if (cpuctx->recursion[rctx]) {
+		put_cpu_var(perf_cpu_context);
 		return -1;
+	}
 
-	(**recursion)++;
+	cpuctx->recursion[rctx]++;
+	barrier();
 
-	return 0;
+	return rctx;
 }
 EXPORT_SYMBOL_GPL(perf_swevent_get_recursion_context);
 
-void perf_swevent_put_recursion_context(int *recursion)
+void perf_swevent_put_recursion_context(int rctx)
 {
-	(*recursion)--;
+	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
+	barrier();
+	cpuctx->recursion[rctx]++;
+	put_cpu_var(perf_cpu_context);
 }
 EXPORT_SYMBOL_GPL(perf_swevent_put_recursion_context);
 
-static void __do_perf_sw_event(enum perf_type_id type, u32 event_id,
-			       u64 nr, int nmi,
-			       struct perf_sample_data *data,
-			       struct pt_regs *regs)
+static void do_perf_sw_event(enum perf_type_id type, u32 event_id,
+				    u64 nr, int nmi,
+				    struct perf_sample_data *data,
+				    struct pt_regs *regs)
 {
+	struct perf_cpu_context *cpuctx;
 	struct perf_event_context *ctx;
-	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
 
+	cpuctx = &__get_cpu_var(perf_cpu_context);
 	rcu_read_lock();
 	perf_swevent_ctx_event(&cpuctx->ctx, type, event_id,
 				 nr, nmi, data, regs);
@@ -3921,34 +3926,22 @@ static void __do_perf_sw_event(enum perf_type_id type, u32 event_id,
 	rcu_read_unlock();
 }
 
-static void do_perf_sw_event(enum perf_type_id type, u32 event_id,
-				    u64 nr, int nmi,
-				    struct perf_sample_data *data,
-				    struct pt_regs *regs)
-{
-	int *recursion;
-
-	preempt_disable();
-
-	if (perf_swevent_get_recursion_context(&recursion))
-		goto out;
-
-	__do_perf_sw_event(type, event_id, nr, nmi, data, regs);
-
-	perf_swevent_put_recursion_context(recursion);
-out:
-	preempt_enable();
-}
-
 void __perf_sw_event(u32 event_id, u64 nr, int nmi,
 			    struct pt_regs *regs, u64 addr)
 {
 	struct perf_sample_data data;
+	int rctx;
+
+	rctx = perf_swevent_get_recursion_context();
+	if (rctx < 0)
+		return;
 
 	data.addr = addr;
 	data.raw  = NULL;
 
 	do_perf_sw_event(PERF_TYPE_SOFTWARE, event_id, nr, nmi, &data, regs);
+
+	perf_swevent_put_recursion_context(rctx);
 }
 
 static void perf_swevent_read(struct perf_event *event)
@@ -4172,7 +4165,7 @@ void perf_tp_event(int event_id, u64 addr, u64 count, void *record,
 		regs = task_pt_regs(current);
 
 	/* Trace events already protected against recursion */
-	__do_perf_sw_event(PERF_TYPE_TRACEPOINT, event_id, count, 1,
+	do_perf_sw_event(PERF_TYPE_TRACEPOINT, event_id, count, 1,
 				&data, regs);
 }
 EXPORT_SYMBOL_GPL(perf_tp_event);