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Subject[PATCH -tip v2 5/9] kprobes: Inverse taking of module_mutex with kprobe_mutex
Date
From: Steven Rostedt <srostedt@redhat.com>

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.

Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.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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