Subject: Re: linux-next: build failure after merge of the tty tree

From: Charalampos Mitrodimas <[email-masked]>
Date: Wed, 01 Oct 2025 00:00:04 +0000

Stephen Rothwell <[email-masked]> writes:

> Hi all,
>
> After merging the tty tree, today's linux-next build (x86_64
> modules_install) failed like this:
>
> depmod: ERROR: Cycle detected: 8250 -> 8250_base -> 8250
> depmod: ERROR: Found 2 modules in dependency cycles!

The cycle was introduced by commit

  b20d6576cdb3 ("serial: 8250: export RSA functions")

which exported RSA functions from 8250.ko to 8250_base.ko to fix this
issue:

  ERROR: modpost: "rsa_autoconfig" [drivers/tty/serial/8250/8250_base.ko] undefined!
  ERROR: modpost: "rsa_reset" [drivers/tty/serial/8250/8250_base.ko] undefined!
  ERROR: modpost: "rsa_disable" [drivers/tty/serial/8250/8250_base.ko] undefined!
  ERROR: modpost: "rsa_enable" [drivers/tty/serial/8250/8250_base.ko] undefined!

which was a regression introduced in this patchset[1].

Before this patchset there's no issue at all:

  INSTALL /tmp/test_cycle/lib/modules/6.16.0-rc2/kernel/drivers/tty/serial/8250/8250.ko
  INSTALL /tmp/test_cycle/lib/modules/6.16.0-rc2/kernel/drivers/tty/serial/8250/8250_base.ko
  INSTALL /tmp/test_cycle/lib/modules/6.16.0-rc2/kernel/drivers/tty/serial/8250/8250_exar.ko
  INSTALL /tmp/test_cycle/lib/modules/6.16.0-rc2/kernel/drivers/tty/serial/8250/8250_lpss.ko
  INSTALL /tmp/test_cycle/lib/modules/6.16.0-rc2/kernel/drivers/tty/serial/8250/8250_mid.ko
  INSTALL /tmp/test_cycle/lib/modules/6.16.0-rc2/kernel/drivers/tty/serial/8250/8250_pci.ko
  INSTALL /tmp/test_cycle/lib/modules/6.16.0-rc2/kernel/drivers/tty/serial/8250/8250_pericom.ko
  INSTALL /tmp/test_cycle/lib/modules/6.16.0-rc2/kernel/drivers/tty/serial/serial_base.ko

So circular dependency landed in b20d6576cdb3 since 8250_base already
depends on 8250.

I'm guessing the fix would be to merge 8250_base.ko into 8250.ko in
drivers/tty/serial/8250/Makefile?

Stephen, I mistakenly sent this off-list to you, ignore it.

[1]: https://lore.kernel.org/all/[email-masked]/

>
> I can't see what would have caused this (it actually appeared yesterday).
> I am not even sure it is something in the tty tree.