linux-kernel - [tip:perf/core] kprobes: Inverse taking of module_mutex with kprobe

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Message-ID: <tip-72ef3794c5cd5f5f0e6355c24a529224c449cd14@git.kernel.org>
Date:	Tue, 21 Aug 2012 08:09:58 -0700
From:	tip-bot for Steven Rostedt <srostedt@...hat.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	fche@...hat.com, mingo@...hat.com, linux-kernel@...r.kernel.org,
	hpa@...or.com, mingo@...nel.org, ananth@...ibm.com,
	masami.hiramatsu.pt@...achi.com, fweisbec@...il.com,
	rostedt@...dmis.org, akpm@...ux-foundation.org,
	srostedt@...hat.com, tglx@...utronix.de
Subject: [tip:perf/core] kprobes:
  Inverse taking of module_mutex with kprobe_mutex

Commit-ID:  72ef3794c5cd5f5f0e6355c24a529224c449cd14
Gitweb:     http://git.kernel.org/tip/72ef3794c5cd5f5f0e6355c24a529224c449cd14
Author:     Steven Rostedt <srostedt@...hat.com>
AuthorDate: Tue, 5 Jun 2012 19:28:14 +0900
Committer:  Steven Rostedt <rostedt@...dmis.org>
CommitDate: Tue, 31 Jul 2012 10:29:55 -0400

kprobes: Inverse taking of module_mutex with kprobe_mutex

Currently module_mutex is taken before kprobe_mutex, but this
can cause issues when we have kprobes register ftrace, as the ftrace
mutex is taken before enabling a tracepoint, which currently takes
the module mutex.

If module_mutex is taken before kprobe_mutex, then we can not
have kprobes use the ftrace infrastructure.

There seems to be no reason that the kprobe_mutex can't be taken
before the module_mutex. Running lockdep shows that it is safe
among the kernels I've run.

Link: http://lkml.kernel.org/r/20120605102814.27845.21047.stgit@localhost.localdomain

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
Cc: "Frank Ch. Eigler" <fche@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/kprobes.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index c62b854..7a8a122 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -561,9 +561,9 @@ static __kprobes void kprobe_optimizer(struct work_struct *work)
 {
 	LIST_HEAD(free_list);
 
+	mutex_lock(&kprobe_mutex);
 	/* Lock modules while optimizing kprobes */
 	mutex_lock(&module_mutex);
-	mutex_lock(&kprobe_mutex);
 
 	/*
 	 * Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
@@ -586,8 +586,8 @@ static __kprobes void kprobe_optimizer(struct work_struct *work)
 	/* Step 4: Free cleaned kprobes after quiesence period */
 	do_free_cleaned_kprobes(&free_list);
 
-	mutex_unlock(&kprobe_mutex);
 	mutex_unlock(&module_mutex);
+	mutex_unlock(&kprobe_mutex);
 
 	/* Step 5: Kick optimizer again if needed */
 	if (!list_empty(&optimizing_list) || !list_empty(&unoptimizing_list))
--
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