[PATCH] perf_events: fix errors path in perf_output_begin()

From: Stephane Eranian <eranian@google.com>
To: linux-kernel@vger.kernel.org
Cc: peterz@infradead.org, mingo@elte.hu, paulus@samba.org,
	davem@davemloft.net, fweisbec@gmail.com, acme@infradead.org,
	perfmon2-devel@lists.sf.net, eranian@gmail.com,
	eranian@google.com
Subject: [PATCH] perf_events: fix errors path in perf_output_begin()
Date: Mon, 17 May 2010 12:46:01 +0200	[thread overview]
Message-ID: <4bf11ea4.dd29e30a.026d.4627@mx.google.com> (raw)

  In case the sampling buffer has no "payload" pages, nr_pages is 0.
  The problem is that the error path in perf_output_begin() skips to
  a label which assumes perf_output_lock() has been issued which is
  not the case. That triggers a WARN_ON() is perf_output_unlock().

  This patch fixes the problem by adding a new label and skipping
  perf_task_unlock() in case data->nr_pages is 0. 

  Signed-off-by: Stephane Eranian <eranian@google.com>

--

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index a4fa381..95137b6 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3035,8 +3035,10 @@ int perf_output_begin(struct perf_output_handle *handle,
 	handle->nmi	= nmi;
 	handle->sample	= sample;
 
-	if (!data->nr_pages)
-		goto fail;
+	if (!data->nr_pages) {
+		atomic_inc(&data->lost);
+		goto out;
+	}
 
 	have_lost = atomic_read(&data->lost);
 	if (have_lost)
