Re: [PATCH 00/19] printk cleanup - part 3

[Marcos Paulo de Souza <mpdesouza@suse.com>]

On Mon, 2026-01-05 at 14:08 +0000, Daniel Thompson wrote:
> On Mon, Jan 05, 2026 at 12:52:14PM +0000, Daniel Thompson wrote:
> > Hi Marcos
> > 
> > On Sat, Dec 27, 2025 at 09:16:07AM -0300, Marcos Paulo de Souza
> > wrote:
> > > The parts 1 and 2 can be found here [1] and here[2].
> > > 
> > > The changes proposed in this part 3 are mostly to clarify the
> > > usage of
> > > the interfaces for NBCON, and use the printk helpers more
> > > broadly.
> > > Besides it, it also introduces a new way to register consoles
> > > and drop thes the CON_ENABLED flag. It seems too much, but in
> > > reality
> > > the changes are not complex, and as the title says, it's
> > > basically a
> > > cleanup without changing the functional changes.
> > 
> > I ran this patchset through the kgdb test suite and I'm afraid it
> > is
> > reporting functional changes.
> > 
> > Specifically the earlycon support for kdb has regressed (FWIW the
> > problem bisects down to the final patch in the series where
> > CON_ENABLED
> > is removed).
> > 
> > Reproduction on x86-64 KVM outside of the test suite should be
> > easy:
> > 
> >     make defconfig
> >     scripts/config \
> >         --enable DEBUG_INFO \
> > 	--enable DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT \
> > 	--enable DEBUG_FS \
> > 	--enable KALLSYMS_ALL \
> > 	--enable MAGIC_SYSRQ \
> > 	--enable KGDB \
> > 	--enable KGDB_TESTS \
> > 	--enable KGDB_KDB \
> > 	--enable KDB_KEYBOARD \
> > 	--enable LKDTM \
> > 	--enable SECURITY_LOCKDOWN_LSM
> >     make olddefconfig
> >     make -j$(nproc)
> >     qemu-system-x86_64 \
> >         -m 1G -smp 2 -nographic \
> > 	-kernel arch/x86/boot/bzImage \
> > 	-append "console=ttyS0,115200 kgdboc=ttyS0
> > earlycon=uart8250,io,0x3f8 kgdboc_earlycon kgdbwait"
> 
> Actually I realized there was a simpler reproduction (hinted at by
> the
> missing "printk: legacy bootconsole [uart8250] enabled" in the
> regressed
> case). It looks like the earlycon simply doesn't work and that means
> the
> reproduction doesn't require anything related to kgdb at all. Simply:
> 
>     make defconfig
>     make -j$(nproc)
>     qemu-system-x86_64 -m 1G -smp 2 -nographic -kernel
> arch/x86/boot/bzImage \
>         -append "earlycon=uart8250,io,0x3f8"
> 
> With the part 3 patchset applied I get no output from the earlycon
> (without the patch set I get the early boot messages which, as
> expected,
> stop when tty0 comes up).

Hi Daniel, sorry for the late reply! Lots of things to check lately :)

Ok, I reproduced here, thanks a lot for testing kgdboc, it's a quick
way to check that the new register_console_force is not working. Let me
take a look to find what's wrong. Thanks a lot for finding this issue!

> 
> 
> Daniel.