netdev - Re: modprobe returns 0 upon -EEXIST from insmod

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Message-ID: <edfed2af-8b4d-4afb-b999-5c46b7d46fba@csgroup.eu>
Date: Mon, 18 Aug 2025 12:07:18 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Phil Sutter <phil@....cc>, netfilter-devel@...r.kernel.org,
 coreteam@...filter.org
Cc: linux-modules@...r.kernel.org, Yi Chen <yiche@...hat.com>,
 netdev@...r.kernel.org
Subject: Re: modprobe returns 0 upon -EEXIST from insmod

[+ Netfilter lists]

Hi Phil

Le 18/08/2025 à 11:34, Phil Sutter a écrit :
> [Vous ne recevez pas souvent de courriers de phil@....cc. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> Hi Christophe,
> 
> On Sun, Aug 17, 2025 at 05:54:27PM +0200, Christophe Leroy wrote:
>> Le 17/08/2025 à 01:33, Phil Sutter a écrit :
>>> [Vous ne recevez pas souvent de courriers de phil@....cc. D?couvrez pourquoi ceci est important ? https://aka.ms/LearnAboutSenderIdentification ]
>>>
>>> Hi,
>>>
>>> I admittedly didn't fully analyze the cause, but on my system a call to:
>>>
>>> # insmod /lib/module/$(uname -r)/kernel/net/netfilter/nf_conntrack_ftp.ko
>>>
>>> fails with -EEXIST (due to a previous call to 'nfct add helper ftp inet
>>> tcp'). A call to:
>>>
>>> # modprobe nf_conntrack_ftp
>>>
>>> though returns 0 even though module loading fails. Is there a bug in
>>> modprobe error status handling?
>>>
>>
>> Read the man page : https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flinux.die.net%2Fman%2F8%2Fmodprobe&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C34b49eb3d0544fc683e608ddde3a75b2%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638911064858807750%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=%2F70LV37Zb%2FNeiBV59y9rvkLGh0xsqga08Nl3c5%2BVU5I%3D&reserved=0
>>
>> In the man page I see:
>>
>>              Normally, modprobe will succeed (and do nothing) if told to
>> insert a module which is already present or to remove a module which
>> isn't present.
> 
> This is not a case of already inserted module, it is not loaded before
> the call to modprobe. It is the module_init callback
> nf_conntrack_ftp_init() which returns -EEXIST it received from
> nf_conntrack_helpers_register().
> 
> Can't user space distinguish the two causes of -EEXIST? Or in other
> words, is use of -EEXIST in module_init callbacks problematic?

So if I understand correctly the load fails because it is in conflict 
with another module ?

Then I think the error returned by nf_conntrack_helpers_register() 
shouldn't be EEXIST but probably EBUSY.

Christophe