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Message-ID: <20130702193425.GA8813@redhat.com>
Date: Tue, 2 Jul 2013 21:34:25 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Steven Rostedt <rostedt@...dmis.org>
Cc: "zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
Jiri Olsa <jolsa@...hat.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: PATCH? trace_remove_event_call() should fail if call is active
To remind/summarise, the usage of unregister_trace_probe() in
trace_kprobe.c and trace_uprobe.c is racy.
unregister_trace_probe() checks trace_probe_is_enabled() but
we can't trust the result, we can race with kprobe_register()
which is going to set TP_FLAG_TRACE/PROFILE.
And we can't add the new lock (or reuse probe_lock) to avoid
the race. kprobe_register() is called under event_mutex, so
unregister_trace_probe() can't hold this new lock around
unregister_probe_event() which takes event_mutex.
And we shouldn't shift event_mutex from trace_remove_event_call()
to its callers, this lock should be private to the core tracing
code.
Masami, Steven. What do you think about the patch below?
To simplify, lets ignore trace_module_remove_events() which calls
__trace_remove_event_call() too, although at first glance this
case should be fine too.
It really seems to me that trace_remove_event_call() should not
succeed if this ftrace_event_call is "active". Even if we forget
about perf, ftrace_event_enable_disable(file, 0) doesn't guarantee
reg(call, TRACE_REG_UNREGISTER) if SOFT_MODE is set.
If something like this patch can work then we can fix trace_kprobe.
unregister_trace_probe() can do unregister_probe_event() first and
abort if trace_remove_event_call() fails.
As for release_all_trace_probes(), we lose the all-or-nothing
semantics, but probably this is fine.
Or I misunderstood this logic completely?
Oleg.
-------------------------------------------------------------------------------
In essence this change is one-liner, it does
- ftrace_event_enable_disable(file);
+ if (file->flags & FTRACE_EVENT_FL_ENABLED)
+ return -EBUSY;
and propagates the error.
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 4372658..f98ab06 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -332,7 +332,7 @@ extern int trace_define_field(struct ftrace_event_call *call, const char *type,
const char *name, int offset, int size,
int is_signed, int filter_type);
extern int trace_add_event_call(struct ftrace_event_call *call);
-extern void trace_remove_event_call(struct ftrace_event_call *call);
+extern int trace_remove_event_call(struct ftrace_event_call *call);
#define is_signed_type(type) (((type)(-1)) < (type)1)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 27963e2..876957c 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1473,15 +1473,20 @@ static void remove_event_from_tracers(struct ftrace_event_call *call)
} while_for_each_event_file();
}
-static void event_remove(struct ftrace_event_call *call)
+static int event_remove(struct ftrace_event_call *call)
{
struct trace_array *tr;
struct ftrace_event_file *file;
+#ifdef CONFIG_PERF_EVENTS
+ if (call->perf_refcount)
+ return -EBUSY;
+#endif
do_for_each_event_file(tr, file) {
if (file->event_call != call)
continue;
- ftrace_event_enable_disable(file, 0);
+ if (file->flags & FTRACE_EVENT_FL_ENABLED)
+ return -EBUSY;
/*
* The do_for_each_event_file() is
* a double loop. After finding the call for this
@@ -1495,6 +1500,7 @@ static void event_remove(struct ftrace_event_call *call)
__unregister_ftrace_event(&call->event);
remove_event_from_tracers(call);
list_del(&call->list);
+ return 0;
}
static int event_init(struct ftrace_event_call *call)
@@ -1604,21 +1610,30 @@ int trace_add_event_call(struct ftrace_event_call *call)
/*
* Must be called under locking both of event_mutex and trace_event_sem.
*/
-static void __trace_remove_event_call(struct ftrace_event_call *call)
+static int __trace_remove_event_call(struct ftrace_event_call *call)
{
- event_remove(call);
- trace_destroy_fields(call);
- destroy_preds(call);
+ int err = event_remove(call);
+
+ if (!err) {
+ trace_destroy_fields(call);
+ destroy_preds(call);
+ }
+
+ return err;
}
/* Remove an event_call */
-void trace_remove_event_call(struct ftrace_event_call *call)
+int trace_remove_event_call(struct ftrace_event_call *call)
{
+ int err;
+
mutex_lock(&event_mutex);
down_write(&trace_event_sem);
- __trace_remove_event_call(call);
+ err = __trace_remove_event_call(call);
up_write(&trace_event_sem);
mutex_unlock(&event_mutex);
+
+ return err;
}
#define for_each_event(event, start, end) \
--
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