linux-kernel - Re: Module loading problem since 5.3

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Message-ID: <20191014144440.GG35313@google.com>
Date:   Mon, 14 Oct 2019 15:44:40 +0100
From:   Matthias Maennich <maennich@...gle.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Jessica Yu <jeyu@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: Module loading problem since 5.3

Hi Luis!

On Mon, Oct 14, 2019 at 08:52:35AM +0000, Luis Chamberlain wrote:
>On Fri, Oct 11, 2019 at 09:26:05PM +0200, Heiner Kallweit wrote:
>> On 10.10.2019 19:15, Luis Chamberlain wrote:
>> >
>> >
>> > On Thu, Oct 10, 2019, 6:50 PM Heiner Kallweit <hkallweit1@...il.com <mailto:hkallweit1@...il.com>> wrote:
>> >
>> >        MODULE_SOFTDEP("pre: realtek")
>> >
>> >     Are you aware of any current issues with module loading
>> >     that could cause this problem?
>> >
>> >
>> > Nope. But then again I was not aware of MODULE_SOFTDEP(). I'd encourage an extension to lib/kmod.c or something similar which stress tests this. One way that comes to mind to test this is to allow a new tests case which loads two drives which co depend on each other using this macro. That'll surely blow things up fast. That is, the current kmod tests uses request_module() or get_fs_type(), you'd want a new test case with this added using then two new dummy test drivers with the macro dependency.
>> >
>> > If you want to resolve this using a more tested path, you could have request_module() be used as that is currently tested. Perhaps a test patch for that can rule out if it's the macro magic which is the issue.
>> >
>> >   Luis
>>
>> Maybe issue is related to a bug in introduction of symbol namespaces, see here:
>> https://lkml.org/lkml/2019/10/11/659
>
>Can you have your user with issues either revert 8651ec01daed or apply the fixes
>mentioned by Matthias to see if that was the issue?
>
>Matthias what module did you run into which let you run into the issue
>with depmod? I ask as I think it would be wise for us to add a test case
>using lib/test_kmod.c and tools/testing/selftests/kmod/kmod.sh for the
>regression you detected.

The depmod warning can be reproduced when using a symbol that is built
into vmlinux and used from a module. E.g. with CONFIG_USB_STORAGE=y and
CONFIG_USB_UAS=m, the symbol `usb_stor_adjust_quirks` is built in with
namespace USB_STORAGE and depmod stumbles upon this emitting the
following warning (e.g. during make modules_install).

  depmod: WARNING: [...]/uas.ko needs unknown symbol usb_stor_adjust_quirks

As there is another (less intrusive) way of implementing the namespace
feature, I posted a patch series [1] on last Thursday that should
mitigate the issue as the ksymtab entries depmod eventually relies on
are no longer carrying the namespace in their names.

Cheers,
Matthias

[1] https://lore.kernel.org/lkml/20191010151443.7399-1-maennich@google.com/

>
>  Luis