Re: [PATCH 17/17] module: Prevent module removal racing with text_poke()

[H. Peter Anvin]

On 1/17/19 10:07 AM, Nadav Amit wrote:
>> On Jan 16, 2019, at 11:54 PM, Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
>>
>> On Wed, 16 Jan 2019 16:32:59 -0800
>> Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> wrote:
>>
>>> From: Nadav Amit <namit@xxxxxxxxxx>
>>>
>>> It seems dangerous to allow code modifications to take place
>>> concurrently with module unloading. So take the text_mutex while the
>>> memory of the module is freed.
>>
>> At that point, since the module itself is removed from module list,
>> it seems no actual harm. Or would you have any concern?
> 
> So it appears that you are right and all the users of text_poke() and
> text_poke_bp() do install module notifiers, and remove the module from their
> internal data structure when they are done (*). As long as they prevent
> text_poke*() to be called concurrently (e.g., using jump_label_lock()),
> everything is fine.
> 
> Having said that, the question is whether you âtrustâ text_poke*() users to
> do so. text_poke() description does not day explicitly that you need to
> prevent modules from being removed.
> 
> What do you say?
> 

Please make it explicit.

	-hpa