linux-kernel - [PATCH v2 1/5] [BUGFIX] tracing: Returns -EBUSY when event_enable

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Date:	Wed, 22 May 2013 11:19:09 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com, Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Tom Zanussi <tom.zanussi@...el.com>
Subject: [PATCH v2 1/5] [BUGFIX] tracing: Returns -EBUSY when
 event_enable_func fails to get module

Since try_module_get returns false( = 0) when it fails to
pindown a module, event_enable_func() returns 0 which means
"succeed". This can cause a kernel panic when the entry
is removed, because the event is already released.

This fixes the bug by returning -EBUSY, because the reason
why it fails is under removing module at that time.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Ingo Molnar <mingo@...hat.com>
---
 kernel/trace/trace_events.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 7a0cf68..27963e2 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -2072,8 +2072,10 @@ event_enable_func(struct ftrace_hash *hash,
  out_reg:
 	/* Don't let event modules unload while probe registered */
 	ret = try_module_get(file->event_call->mod);
-	if (!ret)
+	if (!ret) {
+		ret = -EBUSY;
 		goto out_free;
+	}
 
 	ret = __ftrace_event_enable_disable(file, 1, 1);
 	if (ret < 0)

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