linux-kernel - Re: [patch] module: potential deadlock in error path

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Message-ID: <CA+55aFzEkSOWL13cX2xaYttPF5=Qpvya9Yapk-RC8KQ5=QJk+w@mail.gmail.com>
Date:	Sun, 20 Jan 2013 17:56:14 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Dan Carpenter <dan.carpenter@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kernel-janitors <kernel-janitors@...r.kernel.org>,
	Alexander Graf <agraf@...e.de>,
	Prarit Bhargava <prarit@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [patch] module: potential deadlock in error path

On Sun, Jan 20, 2013 at 5:20 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> Dan Carpenter <dan.carpenter@...cle.com> writes:
>> We take the lock twice if we hit this goto.
>>
>> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
>
> Damn, just pushed that to Linus: should have read mail first.
>
> I've added this, thanks.

I'm not pulling this. It seems stupid.

Why isn't the fix just this (whitespace-damaged, cut-and-pasted)
one-liner instead? I may be blind, but as far as I cal tell, there's
exactly one single place we do that "giti ddebug_cleanup", and it
wants to unlock the mutex, so we should just move the unlock down one
line instead.

Hmm? Is there some hidden magic going on that I can't see?

                  Linus

---
diff --git a/kernel/module.c b/kernel/module.c
index d25e359279ae..eab08274ec9b 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3274,8 +3274,8 @@ again:
        /* module_bug_cleanup needs module_mutex protection */
        mutex_lock(&module_mutex);
        module_bug_cleanup(mod);
-       mutex_unlock(&module_mutex);
  ddebug_cleanup:
+       mutex_unlock(&module_mutex);
        dynamic_debug_remove(info->debug);
        synchronize_sched();
        kfree(mod->args);
--
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