am335x: 5.18.x: system stalling

[Ard Biesheuvel]

On Wed, 1 Jun 2022 at 09:59, Arnd Bergmann <arnd at arndb.de> wrote:
>
> On Wed, Jun 1, 2022 at 9:36 AM Yegor Yefremov
> <yegorslists at googlemail.com> wrote:
> > On Tue, May 31, 2022 at 5:23 PM Arnd Bergmann <arnd at arndb.de> wrote:
> > > I've pushed a modified branch now, with that fix on the broken commit,
> > > and another change to make CONFIG_IRQSTACKS user-selectable rather
> > > than always enabled. That should tell us if the problem is in the SMP
> > > patching or in the irqstacks.
> > >
> > > Can you test the top of this branch with CONFIG_IRQSTACKS disabled,
> > > and (if that still stalls) retest the fixed commit f0191ea5c2e5 ("[PART 1]
> > > ARM: implement THREAD_INFO_IN_TASK for uniprocessor systems")?
> >
> > 1. the top of this branch with CONFIG_IRQSTACKS disabled stalls
> > 2. f0191ea5c2e5 with the same config - not
>
> Ok, perfect, that does narrow down the problem quite a bit: The final
> patch has seven changes, all of which can be done individually because
> in each case the simplified version in f0191ea5c2e5 is meant to run
> the exact same instructions as the version after the change, when running
> on a uniprocessor machine such as your am335x.
>
> You have already shown earlier that the get_current() and
> __my_cpu_offset() functions are not to blame here, as reverting
> only those does not change the behavior.
>
> This leaves the is_smp() check in set_current(), and the
> four macros in <asm/assembler.h>. I don't see anything obviously
> wrong with any of those five, but I would bet on the macros
> here. Can you try bisecting into this commit, maybe reverting
> the changes to set_current and get_current first, and then
> narrowing it down to (hopefully) a single macro that causes the
> problem?
>

set_current() is never called by the primary CPU, which is why the
is_smp() check was removed from there in 57a420435edcb0b94 ("ARM: drop
pointless SMP check on secondary startup path").

So that leaves only the four macros in asm/assembler.h, but I don't
see anything obviously wrong with those either.