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[for-next][PATCH 6/7] ring-buffer: Process commits whenever moving to a new page.

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From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

When crossing over to a new page, commit the current work. This will allow
readers to get data with less latency, and also simplifies the work to get
timestamps working for interrupted events.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/module.c            | 18 ++++++++++++++++--
 kernel/trace/ring_buffer.c |  7 +++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 8f051a106676..c0ae7c18c2fa 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -284,11 +284,25 @@ static void module_assert_mutex(void)
 static void module_assert_mutex_or_preempt(void)
 {
 #ifdef CONFIG_LOCKDEP
+	static int once;
+
 	if (unlikely(!debug_locks))
 		return;
 
-	WARN_ON(!rcu_read_lock_sched_held() &&
-		!lockdep_is_held(&module_mutex));
+	/*
+	 * Would be nice to use WARN_ON_ONCE(), but the warning
+	 * that causes a stack trace may call __module_address()
+	 * which may call here, and we trigger the warning again,
+	 * before the WARN_ON_ONCE() updates its flag.
+	 * To prevent the recursion, we need to open code the
+	 * once logic.
+	 */
+	if (!once &&
+	    unlikely(!rcu_read_lock_sched_held() &&
+		     !lockdep_is_held(&module_mutex))) {
+		once++;
+		WARN_ON(1);
+	}
 #endif
 }
 
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 631541a53baf..95181e36891a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2129,6 +2129,8 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
 	local_sub(length, &tail_page->write);
 }
 
+static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer);
+
 /*
  * This is the slow path, force gcc not to inline it.
  */
@@ -2220,6 +2222,11 @@ rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
 
 	rb_reset_tail(cpu_buffer, tail, info);
 
+	/* Commit what we have for now. */
+	rb_end_commit(cpu_buffer);
+	/* rb_end_commit() decs committing */
+	local_inc(&cpu_buffer->committing);
+
 	/* fail and let the caller try again */
 	return ERR_PTR(-EAGAIN);
 
-- 
2.6.1


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[for-next][PATCH 6/7] ring-buffer: Process commits whenever moving to a new page. Steven Rostedt <rostedt@goodmis.org> - 2015-11-25 17:10 +0100
  Re: [for-next][PATCH 6/7] ring-buffer: Process commits whenever  moving to a new page. Steven Rostedt <rostedt@goodmis.org> - 2015-11-25 21:30 +0100

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