linux-kernel - Re: [PATCH v2 2/2] module: Merge same-name module load requests

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Message-ID: <e070839f-c224-047b-9411-91143c1d8394@redhat.com>
Date:   Mon, 14 Nov 2022 09:57:56 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Prarit Bhargava <prarit@...hat.com>
Cc:     pmladek@...e.com, Petr Pavlu <petr.pavlu@...e.com>,
        linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] module: Merge same-name module load requests

On 12.11.22 02:47, Luis Chamberlain wrote:
> On Wed, Oct 19, 2022 at 02:00:55PM +0200, Petr Pavlu wrote:
>> On 10/18/22 20:33, Luis Chamberlain wrote:
>>> On Sat, Oct 15, 2022 at 11:27:10AM +0200, Petr Pavlu wrote:
>>>> The patch does address a regression observed after commit 6e6de3dee51a
>>>> ("kernel/module.c: Only return -EEXIST for modules that have finished
>>>> loading"). I guess it can have a Fixes tag added to the patch.
>>>>
>>>> I think it is hard to split this patch into parts because the implemented
>>>> "optimization" is the fix.
>>>
>>> git describe --contains 6e6de3dee51a
>>> v5.3-rc1~38^2~6
>>>
>>> I'm a bit torn about this situation. Reverting 6e6de3dee51a would be the
>>> right thing to do, but without it, it still leaves the issue reported
>>> by Prarit Bhargava. We need a way to resolve the issue on stable and
>>> then your optimizations can be applied on top.
>>
>> Simpler could be to do the following:
>>
>> diff --git a/kernel/module/main.c b/kernel/module/main.c
>> index d02d39c7174e..0302ac387e93 100644
>> --- a/kernel/module/main.c
>> +++ b/kernel/module/main.c
>> @@ -2386,7 +2386,8 @@ static bool finished_loading(const char *name)
>>   	sched_annotate_sleep();
>>   	mutex_lock(&module_mutex);
>>   	mod = find_module_all(name, strlen(name), true);
>> -	ret = !mod || mod->state == MODULE_STATE_LIVE;
>> +	ret = !mod || mod->state == MODULE_STATE_LIVE
>> +		|| mod->state == MODULE_STATE_GOING;
>>   	mutex_unlock(&module_mutex);
>>   
>>   	return ret;
>> @@ -2566,7 +2567,8 @@ static int add_unformed_module(struct module *mod)
>>   	mutex_lock(&module_mutex);
>>   	old = find_module_all(mod->name, strlen(mod->name), true);
>>   	if (old != NULL) {
>> -		if (old->state != MODULE_STATE_LIVE) {
>> +		if (old->state == MODULE_STATE_COMING
>> +		    || old->state == MODULE_STATE_UNFORMED) {
>>   			/* Wait in case it fails to load. */
>>   			mutex_unlock(&module_mutex);
>>   			err = wait_event_interruptible(module_wq,
>> @@ -2575,7 +2577,7 @@ static int add_unformed_module(struct module *mod)
>>   				goto out_unlocked;
>>   			goto again;
>>   		}
>> -		err = -EEXIST;
>> +		err = old->state != MODULE_STATE_LIVE ? -EBUSY : -EEXIST;
>>   		goto out;
>>   	}
>>   	mod_update_bounds(mod);
> 
> 
> Prarit, can you verify this still does not break the issue you reported?
> David, does this also fix your issue?

I didn't try, but from a quick glimpse I assume no. Allocating module 
space happens before handling eventual duplicates right now, before a 
module even is "alive" and in the MODULE_STATE_UNFORMED state.

But maybe I am missing something important.

-- 
Thanks,

David / dhildenb