netdev - Re: Module loading problem since 5.3

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Message-ID: <20191018121848.GB11244@42.do-not-panic.com>
Date:   Fri, 18 Oct 2019 12:18:48 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Matthias Maennich <maennich@...gle.com>
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

On Wed, Oct 16, 2019 at 02:37:10PM +0100, Matthias Maennich wrote:
> On Wed, Oct 16, 2019 at 12:50:30PM +0000, Luis Chamberlain wrote:
> > On Mon, Oct 14, 2019 at 03:44:40PM +0100, Matthias Maennich wrote:
> > > 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/
> > 
> > Yes but kmalloc() is built-in, and used by *all* drivers compiled as
> > modules, so why was that an issue?
> 
> I believe you meant, "why was that *not* an issue?".

Right.

> In ksymtab, namespaced symbols had the format
> 
>  __ksymtab_<NAMESPACE>.<symbol>
> 
> while symbols without namespace would still use the old format
> 
>  __ksymtab_<symbol>

Ah, I didn't see the symbol namespace patches, good stuff!

> These are also the names that are extracted into System.map (using
> scripts/mksysmap). Depmod is reading the System.map and for symbols used
> by modules that are in a namespace, it would not find a match as it does
> not understand the namespace notation. Depmod would still not emit a
> warning for symbols without namespace as their format did not change.

Can we have a test case for this to ensure we don't regress on this
again? Or put another way, what test cases were implemented for symbol
namespaces?

  Luis