linux-kernel - Re: [PATCH] static_call: Handle module init failure correctly in static_call_del

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Message-ID: <8bd5e396-7583-435e-bafc-7d092a31f4ff@csgroup.eu>
Date: Fri, 8 Nov 2024 09:12:03 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Mike Rapoport <rppt@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Jinjie Ruan
 <ruanjinjie@...wei.com>, linux-kernel@...r.kernel.org,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Liu Shixin <liushixin2@...wei.com>
Subject: Re: [PATCH] static_call: Handle module init failure correctly in
 static_call_del_module()

Hi Luis,

Le 24/09/2024 à 09:22, Mike Rapoport a écrit :
> On Thu, Sep 19, 2024 at 02:53:34AM -0700, Luis Chamberlain wrote:
>> On Fri, Sep 06, 2024 at 04:24:56PM -0700, Luis Chamberlain wrote:
>>> On Thu, Sep 05, 2024 at 11:44:00AM +0200, Thomas Gleixner wrote:
>>>> Now you at least provided the information that the missing cleanup in
>>>> the init() function is not the problem. So the obvious place to look is
>>>> in the module core code whether there is a failure path _after_
>>>> module->init() returned success.
>>>>
>>>> do_init_module()
>>>>          ret = do_one_initcall(mod->init);
>>>>          ...
>>>> 	ret = module_enable_rodata_ro(mod, true);
>>>> 	if (ret)
>>>> 		goto fail_mutex_unlock;
>>>>
>>>> and that error path does _not_ invoke module->exit(), which is obviously
>>>> not correct. Luis?
>>>
>>> You're spot on this needs fixing.
>>
>> Christophe, this is a regression caused by the second hunk of your commit
>> d1909c0221739 ("module: Don't ignore errors from set_memory_XX()") on v6.9.
>> Sadly there are a few issues with trying to get to call mod->exit():
>>
>> - We should try try_stop_module()  and that can fail
>> - source_list may not be empty and that would block removal
>> - mod->exit may not exist
>>
>> I'm wondering if instead we should try to do the module_enable_rodata_ro()
>> before the init, but that requires a bit more careful evaluation...
> 
> There is ro_after_init section, we can't really make it RO before ->init()
>   

Surprisingly I never received Luis's email allthough I got this answer 
from Mike that I overlooked.

So coming back here from 
https://lore.kernel.org/all/ZyQhbHxDTRXTJgIx@bombadil.infradead.org/

As far as I understand, indeed once init is called it is too late to 
fail, right ? Especially when the module has no exit() path or when 
CONFIG_MODULE_UNLOAD is not built in.

So the only thing we can do then is a big fat warning telling 
set_memory_ro() on ro_after_init memory has failed ?

Maybe we should try and change it to RO then back to RW before calling 
init, to be on a safer side hopping that if change to RO works once it 
will work twice ?

Christophe