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Subject[PATCH 4/5] tracing/events: don't use wake up for events
Date
Impact: fix hard lockup with sched switch events

Some ftrace events, such as sched wakeup, can be traced
while the runqueue lock is hold. Since they are using
trace_current_buffer_unlock_commit(), they call wake_up()
which can try to grab the runqueue lock too, resulting in
a deadlock.

Now for all event, we call a new helper:
trace_nowake_buffer_unlock_commit() which do pretty the same than
trace_current_buffer_unlock_commit() except than it doesn't call
trace_wake_up().

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
kernel/trace/trace.c | 26 +++++++++++++++++++++-----
kernel/trace/trace.h | 2 ++
kernel/trace/trace_events_stage_3.h | 2 +-
3 files changed, 24 insertions(+), 6 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f0e1337..8dddb42 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -860,15 +860,25 @@ static void ftrace_trace_stack(struct trace_array *tr,
static void ftrace_trace_userstack(struct trace_array *tr,
unsigned long flags, int pc);

-void trace_buffer_unlock_commit(struct trace_array *tr,
- struct ring_buffer_event *event,
- unsigned long flags, int pc)
+static inline void __trace_buffer_unlock_commit(struct trace_array *tr,
+ struct ring_buffer_event *event,
+ unsigned long flags, int pc,
+ int wake)
{
ring_buffer_unlock_commit(tr->buffer, event);

ftrace_trace_stack(tr, flags, 6, pc);
ftrace_trace_userstack(tr, flags, pc);
- trace_wake_up();
+
+ if (wake)
+ trace_wake_up();
+}
+
+void trace_buffer_unlock_commit(struct trace_array *tr,
+ struct ring_buffer_event *event,
+ unsigned long flags, int pc)
+{
+ __trace_buffer_unlock_commit(tr, event, flags, pc, 1);
}

struct ring_buffer_event *
@@ -882,7 +892,13 @@ trace_current_buffer_lock_reserve(unsigned char type, unsigned long len,
void trace_current_buffer_unlock_commit(struct ring_buffer_event *event,
unsigned long flags, int pc)
{
- return trace_buffer_unlock_commit(&global_trace, event, flags, pc);
+ return __trace_buffer_unlock_commit(&global_trace, event, flags, pc, 1);
+}
+
+void trace_nowake_buffer_unlock_commit(struct ring_buffer_event *event,
+ unsigned long flags, int pc)
+{
+ return __trace_buffer_unlock_commit(&global_trace, event, flags, pc, 0);
}

void
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index f267723..54fd9bc 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -483,6 +483,8 @@ trace_current_buffer_lock_reserve(unsigned char type, unsigned long len,
unsigned long flags, int pc);
void trace_current_buffer_unlock_commit(struct ring_buffer_event *event,
unsigned long flags, int pc);
+void trace_nowake_buffer_unlock_commit(struct ring_buffer_event *event,
+ unsigned long flags, int pc);

struct trace_entry *tracing_get_trace_entry(struct trace_array *tr,
struct trace_array_cpu *data);
diff --git a/kernel/trace/trace_events_stage_3.h b/kernel/trace/trace_events_stage_3.h
index ebf215e..9a3bd49 100644
--- a/kernel/trace/trace_events_stage_3.h
+++ b/kernel/trace/trace_events_stage_3.h
@@ -222,7 +222,7 @@ static void ftrace_raw_event_##call(proto) \
\
assign; \
\
- trace_current_buffer_unlock_commit(event, irq_flags, pc); \
+ trace_nowake_buffer_unlock_commit(event, irq_flags, pc); \
\
if (call->preds && !filter_match_preds(call, entry)) \
ring_buffer_event_discard(event); \
--
1.6.1


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