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Subject[for-next][PATCH 3/7] tracing: Postpone tracer start-up tests till the system is more robust
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

As tracing can now be enabled very early in boot up, even before some
critical system services (like scheduling), do not run the tracer selftests
until after early_initcall() is performed. If a tracer is registered before
such time, it is saved off in a list and the test is run when the system is
able to handle more diverse functions.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 71 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6757561d9617..68a6f78f6862 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1424,6 +1424,28 @@ static int wait_on_pipe(struct trace_iterator *iter, bool full)
}

#ifdef CONFIG_FTRACE_STARTUP_TEST
+static bool selftests_can_run;
+
+struct trace_selftests {
+ struct list_head list;
+ struct tracer *type;
+};
+
+static LIST_HEAD(postponed_selftests);
+
+static int save_selftest(struct tracer *type)
+{
+ struct trace_selftests *selftest;
+
+ selftest = kmalloc(sizeof(*selftest), GFP_KERNEL);
+ if (!selftest)
+ return -ENOMEM;
+
+ selftest->type = type;
+ list_add(&selftest->list, &postponed_selftests);
+ return 0;
+}
+
static int run_tracer_selftest(struct tracer *type)
{
struct trace_array *tr = &global_trace;
@@ -1434,6 +1456,14 @@ static int run_tracer_selftest(struct tracer *type)
return 0;

/*
+ * If a tracer registers early in boot up (before scheduling is
+ * initialized and such), then do not run its selftests yet.
+ * Instead, run it a little later in the boot process.
+ */
+ if (!selftests_can_run)
+ return save_selftest(type);
+
+ /*
* Run a selftest on this tracer.
* Here we reset the trace buffer, and set the current
* tracer to be this tracer. The tracer can then run some
@@ -1482,6 +1512,47 @@ static int run_tracer_selftest(struct tracer *type)
printk(KERN_CONT "PASSED\n");
return 0;
}
+
+static __init int init_trace_selftests(void)
+{
+ struct trace_selftests *p, *n;
+ struct tracer *t, **last;
+ int ret;
+
+ selftests_can_run = true;
+
+ mutex_lock(&trace_types_lock);
+
+ if (list_empty(&postponed_selftests))
+ goto out;
+
+ pr_info("Running postponed tracer tests:\n");
+
+ list_for_each_entry_safe(p, n, &postponed_selftests, list) {
+ ret = run_tracer_selftest(p->type);
+ /* If the test fails, then warn and remove from available_tracers */
+ if (ret < 0) {
+ WARN(1, "tracer: %s failed selftest, disabling\n",
+ p->type->name);
+ last = &trace_types;
+ for (t = trace_types; t; t = t->next) {
+ if (t == p->type) {
+ *last = t->next;
+ break;
+ }
+ last = &t->next;
+ }
+ }
+ list_del(&p->list);
+ kfree(p);
+ }
+
+ out:
+ mutex_unlock(&trace_types_lock);
+
+ return 0;
+}
+early_initcall(init_trace_selftests);
#else
static inline int run_tracer_selftest(struct tracer *type)
{
--
2.10.2

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