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authorOleg Nesterov <oleg@redhat.com>2013-06-20 19:38:09 +0200
committerSteven Rostedt <rostedt@goodmis.org>2013-07-01 20:34:24 -0400
commit3fe3d6193e7cd7b4dd2bde10772f048bdefea4ee (patch)
treef7623a40ffb23ffab302a8cb9ed6c5716ec1d691 /kernel
parent288e984e622336bab8bc3dfdf2f190816362d9a1 (diff)
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tracing/kprobes: Kill probe_enable_lock
enable_trace_probe() and disable_trace_probe() should not worry about serialization, the caller (perf_trace_init or __ftrace_set_clr_event) holds event_mutex. They are also called by kprobe_trace_self_tests_init(), but this __init function can't race with itself or trace_events.c And note that this code depended on event_mutex even before 41a7dd420c which introduced probe_enable_lock. In fact it assumes that the caller kprobe_register() can never race with itself. Otherwise, say, tp->flags manipulations are racy. Link: http://lkml.kernel.org/r/20130620173809.GA13158@redhat.com Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/trace_kprobe.c43
1 files changed, 20 insertions, 23 deletions
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index c35bebe53ffe..282f86cfd304 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -183,16 +183,15 @@ static struct trace_probe *find_trace_probe(const char *event,
return NULL;
}
+/*
+ * This and enable_trace_probe/disable_trace_probe rely on event_mutex
+ * held by the caller, __ftrace_set_clr_event().
+ */
static int trace_probe_nr_files(struct trace_probe *tp)
{
- struct ftrace_event_file **file;
+ struct ftrace_event_file **file = rcu_dereference_raw(tp->files);
int ret = 0;
- /*
- * Since all tp->files updater is protected by probe_enable_lock,
- * we don't need to lock an rcu_read_lock.
- */
- file = rcu_dereference_raw(tp->files);
if (file)
while (*(file++))
ret++;
@@ -200,8 +199,6 @@ static int trace_probe_nr_files(struct trace_probe *tp)
return ret;
}
-static DEFINE_MUTEX(probe_enable_lock);
-
/*
* Enable trace_probe
* if the file is NULL, enable "perf" handler, or enable "trace" handler.
@@ -211,8 +208,6 @@ enable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
{
int ret = 0;
- mutex_lock(&probe_enable_lock);
-
if (file) {
struct ftrace_event_file **new, **old;
int n = trace_probe_nr_files(tp);
@@ -223,7 +218,7 @@ enable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
GFP_KERNEL);
if (!new) {
ret = -ENOMEM;
- goto out_unlock;
+ goto out;
}
memcpy(new, old, n * sizeof(struct ftrace_event_file *));
new[n] = file;
@@ -246,10 +241,7 @@ enable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
else
ret = enable_kprobe(&tp->rp.kp);
}
-
- out_unlock:
- mutex_unlock(&probe_enable_lock);
-
+ out:
return ret;
}
@@ -282,8 +274,6 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
{
int ret = 0;
- mutex_lock(&probe_enable_lock);
-
if (file) {
struct ftrace_event_file **new, **old;
int n = trace_probe_nr_files(tp);
@@ -292,7 +282,7 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
old = rcu_dereference_raw(tp->files);
if (n == 0 || trace_probe_file_index(tp, file) < 0) {
ret = -EINVAL;
- goto out_unlock;
+ goto out;
}
if (n == 1) { /* Remove the last file */
@@ -303,7 +293,7 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
GFP_KERNEL);
if (!new) {
ret = -ENOMEM;
- goto out_unlock;
+ goto out;
}
/* This copy & check loop copies the NULL stopper too */
@@ -326,10 +316,7 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
else
disable_kprobe(&tp->rp.kp);
}
-
- out_unlock:
- mutex_unlock(&probe_enable_lock);
-
+ out:
return ret;
}
@@ -1214,6 +1201,12 @@ kretprobe_perf_func(struct trace_probe *tp, struct kretprobe_instance *ri,
}
#endif /* CONFIG_PERF_EVENTS */
+/*
+ * called by perf_trace_init() or __ftrace_set_clr_event() under event_mutex.
+ *
+ * kprobe_trace_self_tests_init() does enable_trace_probe/disable_trace_probe
+ * lockless, but we can't race with this __init function.
+ */
static __kprobes
int kprobe_register(struct ftrace_event_call *event,
enum trace_reg type, void *data)
@@ -1379,6 +1372,10 @@ find_trace_probe_file(struct trace_probe *tp, struct trace_array *tr)
return NULL;
}
+/*
+ * Nobody but us can call enable_trace_probe/disable_trace_probe at this
+ * stage, we can do this lockless.
+ */
static __init int kprobe_trace_self_tests_init(void)
{
int ret, warn = 0;