tracing: Allocate the ftrace event profile buffer dynamically

Currently the trace event profile buffer is allocated in the stack. But
this may be too much for the stack, as the events can have large
statically defined field size and can also grow with dynamic arrays.

Allocate two per cpu buffer for all profiled events. The first cpu
buffer is used to host every non-nmi context traces. It is protected
by disabling the interrupts while writing and committing the trace.

The second buffer is reserved for nmi. So that there is no race between
them and the first buffer.

The whole write/commit section is rcu protected because we release
these buffers while deactivating the last profiling trace event.

v2: Move the buffers from trace_event to be global, as pointed by
    Steven Rostedt.

v3: Fix the syscall events to handle the profiling buffer races
    by disabling interrupts, now that the buffers are globals.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>

1 files changed, 60 insertions, 1 deletions

diff --git a/kernel/trace/trace_event_profile.c b/kernel/trace/trace_event_profile.c
index df4a74efd50..3aaa77c3309 100644
--- a/kernel/trace/trace_event_profile.c
+++ b/kernel/trace/trace_event_profile.c
@@ -8,12 +8,52 @@
 #include <linux/module.h>
 #include "trace.h"
 
+/*
+ * We can't use a size but a type in alloc_percpu()
+ * So let's create a dummy type that matches the desired size
+ */
+typedef struct {char buf[FTRACE_MAX_PROFILE_SIZE];} profile_buf_t;
+
+char		*trace_profile_buf;
+char 		*trace_profile_buf_nmi;
+
+/* Count the events in use (per event id, not per instance) */
+static int	total_profile_count;
+
 static int ftrace_profile_enable_event(struct ftrace_event_call *event)
 {
+	char *buf;
+	int ret = -ENOMEM;
+
 	if (atomic_inc_return(&event->profile_count))
 		return 0;
 
-	return event->profile_enable();
+	if (!total_profile_count++) {
+		buf = (char *)alloc_percpu(profile_buf_t);
+		if (!buf)
+			goto fail_buf;
+
+		rcu_assign_pointer(trace_profile_buf, buf);
+
+		buf = (char *)alloc_percpu(profile_buf_t);
+		if (!buf)
+			goto fail_buf_nmi;
+
+		rcu_assign_pointer(trace_profile_buf_nmi, buf);
+	}
+
+	ret = event->profile_enable();
+	if (!ret)
+		return 0;
+
+	kfree(trace_profile_buf_nmi);
+fail_buf_nmi:
+	kfree(trace_profile_buf);
+fail_buf:
+	total_profile_count--;
+	atomic_dec(&event->profile_count);
+
+	return ret;
 }
 
 int ftrace_profile_enable(int event_id)
@@ -36,10 +76,29 @@ int ftrace_profile_enable(int event_id)
 
 static void ftrace_profile_disable_event(struct ftrace_event_call *event)
 {
+	char *buf, *nmi_buf;
+
 	if (!atomic_add_negative(-1, &event->profile_count))
 		return;
 
 	event->profile_disable();
+
+	if (!--total_profile_count) {
+		buf = trace_profile_buf;
+		rcu_assign_pointer(trace_profile_buf, NULL);
+
+		nmi_buf = trace_profile_buf_nmi;
+		rcu_assign_pointer(trace_profile_buf_nmi, NULL);
+
+		/*
+		 * Ensure every events in profiling have finished before
+		 * releasing the buffers
+		 */
+		synchronize_sched();
+
+		free_percpu(buf);
+		free_percpu(nmi_buf);
+	}
 }
 
 void ftrace_profile_disable(int event_id)