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

Steven Rostedt
2015-11-25T16:09:20Z

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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