linux-kernel - Re: [PATCH] livepatch: fix race between enabled_store() and klp_unregister

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Date:	Tue, 1 Dec 2015 15:28:19 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Li Bin <huawei.libin@...wei.com>, sjenning@...hat.com,
	jikos@...nel.org, vojtech@...e.com, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org, guohanjun@...wei.com,
	dingtianhong@...wei.com, xiexiuqi@...wei.com,
	zhouchengming1@...wei.com, Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH] livepatch: fix race between enabled_store() and
 klp_unregister_patch()

On 12/01/2015, 03:13 PM, Petr Mladek wrote:
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -612,7 +612,19 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
>  
>  	patch = container_of(kobj, struct klp_patch, kobj);
>  
> -	mutex_lock(&klp_mutex);
> +	/*
> +	 * Avoid a deadlock with kobject_put(&patch->kobj) that is
> +	 * called under klp_mutex. Bail out when the patch is not
> +	 * longer registered.
> +	 */
> +	if (!mutex_trylock(&klp_mutex)) {

This introduces false positives.
Deleting/enabling/disabling/other_op_under_klp_mutex of an unrelated
patch may now cause enabled_store to fail. Hence I don't like this
approach at all.

thanks,
-- 
js
suse labs
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