[PATCH v2 2/3] tracing/kprobes: Kill probe_enable_lock
From: Oleg Nesterov
Date: Wed Jun 19 2013 - 16:34:38 EST
On 06/18, Oleg Nesterov wrote:
>
> On 06/18, Masami Hiramatsu wrote:
> >
> > Oh, I agree with removing probe_enable_lock itself :)
> > I just concerned only about the exceptional case of __init test
> > function, which can mislead someone to use enable/disable_trace_probe
> > at other racy point.
>
> Ah, understand.
>
> OK, I'll send v2 with the updated comments plus the additional patch
> tomorrow.
So. I'll resend this series, will you ack the v2 below?
I only added a couple of comments, the interdiff is
@@ -1202,6 +1202,12 @@ kretprobe_perf_func(struct trace_probe *
}
#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)
@@ -1367,6 +1373,10 @@ find_trace_probe_file(struct trace_probe
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;
3/3 was updated too, but the only change is s/list_add_rcu/list_add_tail_rcu/,
I won't spam the list but preserve your ack unless you object.
Oleg.
-------------------------------------------------------------------------------
Subject: [PATCH v2] 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.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
kernel/trace/trace_kprobe.c | 43 ++++++++++++++++++++-----------------------
1 files changed, 20 insertions(+), 23 deletions(-)
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index c0af476..3432652 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;
@@ -247,10 +242,7 @@ 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;
}
@@ -283,8 +275,6 @@ 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);
@@ -293,7 +283,7 @@ 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 */
@@ -304,7 +294,7 @@ 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 */
@@ -327,10 +317,7 @@ 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;
}
@@ -1215,6 +1202,12 @@ 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)
@@ -1380,6 +1373,10 @@ 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;
--
1.5.5.1
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