Re: Module loading problem since 5.3

[Matthias Maennich]

On Fri, Oct 18, 2019 at 12:18:48PM +0000, Luis Chamberlain wrote:
> 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@xxxxxxxxx <mailto:hkallweit1@xxxxxxxxx>> wrote:
> > > > > > >
> > > > > > >     Â ÂMODULE_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.
> > > > > > >
> > > > > > > Â 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@xxxxxxxxxx/
> > >
> > > 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?

While modpost and kernel/module.c are the tests at build and runtime
resp. to enforce proper use of symbol namespaces, I could imagine to
test for the proper layout in the ksymtab entries (note, as mentioned
earlier there are some fixes in flight to finalize the layout).
In addition, I could imagine adding a test that tries to load a module
that uses symbols from a namespace without importing it. The kernel
should deny loading or complain about it (depending on the
configuration). These are also some of the test cases I had when working
on that feature. I did not implement these as automated tests though. I
will put that on my list but help with that would be very welcome.

Cheers,
Matthias