Re: [RFC PATCH 1/9] livepatch: simplify disable error path

[Miroslav Benes]

On Mon, 9 Feb 2015, Josh Poimboeuf wrote:

> If registering the function with ftrace has previously succeeded,
> unregistering will almost never fail.  Even if it does, it's not a fatal
> error.  We can still carry on and disable the klp_func from being used
> by removing it from the klp_ops func stack.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

This makes sense, so

Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>

I think this patch could be taken independently of the consistency model. 
If no one else has any objection...

Miroslav

> ---
>  kernel/livepatch/core.c | 67 +++++++++++++------------------------------------
>  1 file changed, 17 insertions(+), 50 deletions(-)
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 9adf86b..081df77 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -322,32 +322,20 @@ static void notrace klp_ftrace_handler(unsigned long ip,
>  	klp_arch_set_pc(regs, (unsigned long)func->new_func);
>  }
>  
> -static int klp_disable_func(struct klp_func *func)
> +static void klp_disable_func(struct klp_func *func)
>  {
>  	struct klp_ops *ops;
> -	int ret;
> -
> -	if (WARN_ON(func->state != KLP_ENABLED))
> -		return -EINVAL;
>  
> -	if (WARN_ON(!func->old_addr))
> -		return -EINVAL;
> +	WARN_ON(func->state != KLP_ENABLED);
> +	WARN_ON(!func->old_addr);
>  
>  	ops = klp_find_ops(func->old_addr);
>  	if (WARN_ON(!ops))
> -		return -EINVAL;
> +		return;
>  
>  	if (list_is_singular(&ops->func_stack)) {
> -		ret = unregister_ftrace_function(&ops->fops);
> -		if (ret) {
> -			pr_err("failed to unregister ftrace handler for function '%s' (%d)\n",
> -			       func->old_name, ret);
> -			return ret;
> -		}
> -
> -		ret = ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0);
> -		if (ret)
> -			pr_warn("function unregister succeeded but failed to clear the filter\n");
> +		WARN_ON(unregister_ftrace_function(&ops->fops));
> +		WARN_ON(ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0));
>  
>  		list_del_rcu(&func->stack_node);
>  		list_del(&ops->node);
> @@ -357,8 +345,6 @@ static int klp_disable_func(struct klp_func *func)
>  	}
>  
>  	func->state = KLP_DISABLED;
> -
> -	return 0;
>  }
>  
>  static int klp_enable_func(struct klp_func *func)
> @@ -419,23 +405,15 @@ err:
>  	return ret;
>  }
>  
> -static int klp_disable_object(struct klp_object *obj)
> +static void klp_disable_object(struct klp_object *obj)
>  {
>  	struct klp_func *func;
> -	int ret;
>  
> -	for (func = obj->funcs; func->old_name; func++) {
> -		if (func->state != KLP_ENABLED)
> -			continue;
> -
> -		ret = klp_disable_func(func);
> -		if (ret)
> -			return ret;
> -	}
> +	for (func = obj->funcs; func->old_name; func++)
> +		if (func->state == KLP_ENABLED)
> +			klp_disable_func(func);
>  
>  	obj->state = KLP_DISABLED;
> -
> -	return 0;
>  }
>  
>  static int klp_enable_object(struct klp_object *obj)
> @@ -451,22 +429,19 @@ static int klp_enable_object(struct klp_object *obj)
>  
>  	for (func = obj->funcs; func->old_name; func++) {
>  		ret = klp_enable_func(func);
> -		if (ret)
> -			goto unregister;
> +		if (ret) {
> +			klp_disable_object(obj);
> +			return ret;
> +		}
>  	}
>  	obj->state = KLP_ENABLED;
>  
>  	return 0;
> -
> -unregister:
> -	WARN_ON(klp_disable_object(obj));
> -	return ret;
>  }
>  
>  static int __klp_disable_patch(struct klp_patch *patch)
>  {
>  	struct klp_object *obj;
> -	int ret;
>  
>  	/* enforce stacking: only the last enabled patch can be disabled */
>  	if (!list_is_last(&patch->list, &klp_patches) &&
> @@ -476,12 +451,8 @@ static int __klp_disable_patch(struct klp_patch *patch)
>  	pr_notice("disabling patch '%s'\n", patch->mod->name);
>  
>  	for (obj = patch->objs; obj->funcs; obj++) {
> -		if (obj->state != KLP_ENABLED)
> -			continue;
> -
> -		ret = klp_disable_object(obj);
> -		if (ret)
> -			return ret;
> +		if (obj->state == KLP_ENABLED)
> +			klp_disable_object(obj);
>  	}
>  
>  	patch->state = KLP_DISABLED;
> @@ -931,7 +902,6 @@ static void klp_module_notify_going(struct klp_patch *patch,
>  {
>  	struct module *pmod = patch->mod;
>  	struct module *mod = obj->mod;
> -	int ret;
>  
>  	if (patch->state == KLP_DISABLED)
>  		goto disabled;
> @@ -939,10 +909,7 @@ static void klp_module_notify_going(struct klp_patch *patch,
>  	pr_notice("reverting patch '%s' on unloading module '%s'\n",
>  		  pmod->name, mod->name);
>  
> -	ret = klp_disable_object(obj);
> -	if (ret)
> -		pr_warn("failed to revert patch '%s' on module '%s' (%d)\n",
> -			pmod->name, mod->name, ret);
> +	klp_disable_object(obj);
>  
>  disabled:
>  	klp_free_object_loaded(obj);
> -- 
> 2.1.0
> 
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