Re: [PATCH 0/2] clk: kunit: Fix the lockdep warnings

[Maxime Ripard]

Hi Stephen,

On Wed, Aug 23, 2023 at 12:50:46PM -0700, Stephen Boyd wrote:
> Quoting Maxime Ripard (2023-08-21 04:16:12)
> > Hi Stephen,
> > 
> > On Wed, Aug 09, 2023 at 06:37:30PM -0700, Stephen Boyd wrote:
> > > Quoting Stephen Boyd (2023-08-09 16:21:50)
> > > > +kunit-dev
> > > > 
> > > > Quoting Maxime Ripard (2023-07-21 00:09:31)
> > > > > Hi,
> > > > > 
> > > > > Here's a small series to address the lockdep warning we have when
> > > > > running the clk kunit tests with lockdep enabled.
> > > > > 
> > > > > For the record, it can be tested with:
> > > > > 
> > > > > $ ./tools/testing/kunit/kunit.py run \
> > > > >     --kunitconfig=drivers/clk \
> > > > >     --cross_compile aarch64-linux-gnu- --arch arm64 \
> > > > >     --kconfig_add CONFIG_DEBUG_KERNEL=y \
> > > > >     --kconfig_add CONFIG_PROVE_LOCKING=y
> > > > > 
> > > > > Let me know what you think,
> > > > 
> > > > Thanks for doing this. I want to roll these helpers into the clk_kunit.c
> > > > file that I had created for some other clk tests[1]. That's mostly
> > > > because clk.c is already super long and adding kunit code there makes
> > > > that problem worse. I'll try to take that patch out of the rest of the
> > > > series and then add this series on top and resend.
> > > > 
> > > > I don't know what to do about the case where CONFIG_KUNIT=m though. We
> > > > have to export clk_prepare_lock/unlock()? I really don't want to do that
> > > > even if kunit is enabled (see EXPORT_SYMBOL_IF_KUNIT). Maybe if there
> > > > was a GPL version of that, so proprietary modules can't get at kernel
> > > > internals on kunit enabled kernels.
> > > > 
> > > > But I also like the approach taken here of adding a small stub around
> > > > the call to make sure a test is running. Maybe I'll make a kunit
> > > > namespaced exported gpl symbol that bails if a test isn't running and
> > > > calls the clk_prepare_lock/unlock functions inside clk.c and then move
> > > > the rest of the code to clk_kunit.c to get something more strict.
> > > > 
> > > 
> > > What if we don't try to do any wrapper or export symbols and test
> > > __clk_determine_rate() how it is called from the clk framework? The
> > > downside is the code is not as simple because we have to check things
> > > from within the clk_ops::determine_rate(), but the upside is that we can
> > > avoid exporting internal clk APIs or wrap them so certain preconditions
> > > are met like requiring them to be called from within a clk_op.
> > 
> > The main reason for that test was linked to commit 262ca38f4b6e ("clk:
> > Stop forwarding clk_rate_requests to the parent"). Prior to it, if a
> > clock had CLK_SET_RATE_PARENT, we could end up with its parent's parent
> > hw struct and rate in best_parent_*.
> > 
> > So that test was mostly about making sure that __clk_determine_rate will
> > properly set the best_parent fields to match the clock's parent.
> > 
> > If we do a proper clock that uses __clk_determine_rate, we lose the
> > ability to check the content of the clk_rate_request returned by
> > __clk_determine_rate. It's up to you to tell whether it's a bad thing or
> > not :)
> 
> I'm a little confused here. Was the test trying to check the changed
> lines in clk_core_round_rate_nolock() that were made in commit
> 262ca38f4b6e under the CLK_SET_RATE_PARENT condition?

That's what I was trying to test, yeah. Not necessarily this function in
particular (there's several affected), but at least we would get
something sane in a common case.

> From what I can tell that doesn't get tested here.
> 
> Instead, the test calls __clk_determine_rate() that calls
> clk_core_round_rate_nolock() which falls into the clk_core_can_round()
> condition because the hw has clk_dummy_single_parent_ops which has
> .determine_rate op set to __clk_mux_determine_rate_closest(). Once we
> find that the clk can round, we call __clk_mux_determine_rate_closest().

clk_mux_determine_rate_flags was also affected by the same issue.

> This patch still calls __clk_mux_determine_rate_closest() like
> __clk_determine_rate() was doing in the test, and checks that the
> request structure has the expected parent in the req->best_parent_hw.
> 
> If we wanted to test the changed lines in clk_core_round_rate_nolock()
> we should have called __clk_determine_rate() on a clk_hw that didn't
> have a .determine_rate or .round_rate clk_op. Then it would have fallen
> into the if (core->flags & CLK_SET_RATE_PARENT) condition in
> clk_core_round_rate_nolock() and made sure that the request structure
> returned was properly forwarded to the parent.
>
> We can still do that by making a child of the leaf, set clk_ops on that
> to be this new determine_rate clk op that calls to the parent (the leaf
> today), and make that leaf clk not have any determine_rate clk_op. Then
> we will fall into the CLK_SET_RATE_PARENT condition and can make sure
> the request structure returned points at the parent instead of the mux.

But you're right clk_core_round_rate_nolock() wasn't properly tested. I
guess, if we find it worth it, we should add a test for that one too?

clk_mux_determine_rate_flags with multiple parents and
CLK_SET_RATE_PARENT was also affected and fixed in the commit mentioned
above.

Maxime

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