Re: [PATCH v3] serial: 8250: Clear CON_PRINTBUFFER on port re-registration

Mark Brown <[email protected]> Thu, 23 Jul 2026 22:55:44 +0100
Newsgroups	org.kernel.vger.linux-serial,org.kernel.vger.linux-kernel
Message-ID	<[email protected]>
On Fri, May 22, 2026 at 06:10:42PM +0800, Fushuai Wang wrote:
> From: Fushuai Wang <[email protected]>
> 
> When two PnP devices map to the same physical port, the serial8250 driver
> removes and re-registers the console structure for the same port.
> 
> During re-registration, the console structure still has CON_PRINTBUFFER set
> from the initial registration, which causes console_init_seq() to set
> console->seq to syslog_seq. This results in re-printing the entire
> system log buffer, which may lead to RCU stall on slow serial consoles.
> 
> Clear CON_PRINTBUFFER when re-registering a port to prevent duplicate
> log printing.

For the past week or more (I think since it was committed) I have been
seeing boot regressions in -next on a wide range of platforms which
bisect to it.  One sample is the VisionFive2 which gets to userspace but
grinds to a halt:

[   16.954602] pci 0001:00:00.0: bridge configuration invalid ([bus 00-00]), reconfiguring
[   16.962739] pci_bus 0001:01: busn_res: [bus 01-ff] end is updated to 01
[   16.969371] pci 0001:00:00.0: PCI bridge to [bus 01]
[   16.974348] pci_bus 0001:00: resource 4 [mem 0x38000000-0x3fffffff]
[   16.980620] pci_bus 0001:00: resource 5 [mem 0x980000000-0x9bfffffff pref]
[   16.987749] pcieport 0001:00:00.0: PME: Signaling with IRQ 66
/bin/sh: can't access tty; job control turned off

Full log:

   https://lava.sirena.org.uk/scheduler/job/3013935#L604

I'm also seeing this on for example pine64plus.  Some platforms have
some WARN_ON()s from DRM which slowed reporting but those don't seem
related.

bisect log, other platforms look similar and converge on the same commit:

git bisect start
# status: waiting for both good and bad commits
# bad: [9eebf259d5352b87080d67758f483583d9e763d7] Add linux-next specific files for 20260723
git bisect bad 9eebf259d5352b87080d67758f483583d9e763d7
# status: waiting for good commit(s), bad commit known
# good: [922cc3121ee3e099ec8d36c468f38cd3dff3308a] Merge branch 'for-linux-next-fixes' of https://gitlab.freedesktop.org/drm/misc/kernel.git
git bisect good 922cc3121ee3e099ec8d36c468f38cd3dff3308a
# good: [a442ff27677c2fdc0c046778a6c12b78cc9561ec] Merge branch 'libcrypto-next' of https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git
git bisect good a442ff27677c2fdc0c046778a6c12b78cc9561ec
# good: [62dd23e06176ab94221cbe269c46483534cf6545] Merge branch 'for-next' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator.git
git bisect good 62dd23e06176ab94221cbe269c46483534cf6545
# good: [cbbe21042d5ae5b70f7bfd02fa345ccdea53b069] Merge branch 'usb-next' of https://git.kernel.org/pub/scm/linux/kernel/git/johan/usb-serial.git
git bisect good cbbe21042d5ae5b70f7bfd02fa345ccdea53b069
# bad: [ed9b79b61e9248ec87c34c0d2f7f2109e7f3a651] Merge branch 'staging-next' of https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
git bisect bad ed9b79b61e9248ec87c34c0d2f7f2109e7f3a651
# bad: [5e110656994217e9816366ae54b83511b55f4f77] Merge branch 'togreg' of https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git
git bisect bad 5e110656994217e9816366ae54b83511b55f4f77
# bad: [d6082d34d41e4bd21dbe39203e2e050016d092e3] Merge branch 'char-misc-next' of https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
git bisect bad d6082d34d41e4bd21dbe39203e2e050016d092e3
# good: [6994c8b4ef95114073a51d6143185bca39d6e5d5] drivers/misc/enclosure: Replace strcpy() + strcat() with snprintf()
git bisect good 6994c8b4ef95114073a51d6143185bca39d6e5d5
# bad: [6e5bd7cc3a2f304a66d294011647d82074421979] serial: qcom-geni: Add tracepoints for Qualcomm GENI serial driver
git bisect bad 6e5bd7cc3a2f304a66d294011647d82074421979
# bad: [7a68b818d56e5c48b90232d59148ef8e716082ae] serdev: acpi: Free resource list at appropriate time
git bisect bad 7a68b818d56e5c48b90232d59148ef8e716082ae
# good: [25b51d1fd3268a219e43608b165098fff7cd9dcd] serial: max310x: register GPIO controller before adding UART ports
git bisect good 25b51d1fd3268a219e43608b165098fff7cd9dcd
# bad: [d338ab1d90603f875c4f7ed223406535378173a5] serial: 8250: Clear CON_PRINTBUFFER on port re-registration
git bisect bad d338ab1d90603f875c4f7ed223406535378173a5
# good: [7a52545d37eb805eb1f3c7e03ff336b12c12f5af] tty: tty_jobctrl: use guard()s in tiocspgrp()
git bisect good 7a52545d37eb805eb1f3c7e03ff336b12c12f5af
# good: [4d105880666ab7f7914a75716d3e95b0d8b879dc] tty: serial: mpc52xx_uart: add bounds check for psc_num array index
git bisect good 4d105880666ab7f7914a75716d3e95b0d8b879dc
# first bad commit: [d338ab1d90603f875c4f7ed223406535378173a5] serial: 8250: Clear CON_PRINTBUFFER on port re-registration
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