user/sven/linux.git/kernel/printk, branch v6.16.2

printk: nbcon: Allow reacquire during panic

2025-08-20T16:41:30Z

[ Upstream commit 571c1ea91a73db56bd94054fabecd0f070dc90db ] If a console printer is interrupted during panic, it will never be able to reacquire ownership in order to perform and cleanup. That in itself is not a problem, since the non-panic CPU will simply quiesce in an endless loop within nbcon_reacquire_nobuf(). However, in this state, platforms that do not support a true NMI to interrupt the quiesced CPU will not be able to shutdown that CPU from within panic(). This then causes problems for such as being unable to load and run a kdump kernel. Fix this by allowing non-panic CPUs to reacquire ownership using a direct acquire. Then the non-panic CPUs can successfullyl exit the nbcon_reacquire_nobuf() loop and the console driver can perform any necessary cleanup. But more importantly, the CPU is no longer quiesced and is free to process any interrupts necessary for panic() to shutdown the CPU. All other forms of acquire are still not allowed for non-panic CPUs since it is safer to have them avoid gaining console ownership that is not strictly necessary. Reported-by: Michael Kelley Closes: https://lore.kernel.org/r/SN6PR02MB4157A4C5E8CB219A75263A17D46DA@SN6PR02MB4157.namprd02.prod.outlook.com Signed-off-by: John Ogness Reviewed-by: Petr Mladek Tested-by: Michael Kelley Link: https://patch.msgid.link/20250606185549.900611-1-john.ogness@linutronix.de Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

Merge tag 'printk-for-6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

2025-03-28T02:22:24Z

Pull printk updates from Petr Mladek: - New option "printk.debug_non_panic_cpus" allows to store printk messages from non-panic CPUs during panic. It might be useful when panic() fails. It is disabled by default because it increases the chance to see the messages printed before panic() and on the panic-CPU. - New build option "CONFIG_NULL_TTY_DEFAULT_CONSOLE" allows to build kernel without the virtual terminal support which prefers ttynull over serial console. - Do not unblank suspended consoles. - Some code clean up. * tag 'printk-for-6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: printk/panic: Add option to allow non-panic CPUs to write to the ring buffer. printk: Add an option to allow ttynull to be a default console device printk: Check CON_SUSPEND when unblanking a console printk: Rename console_start to console_resume printk: Rename console_stop to console_suspend printk: Rename resume_console to console_resume_all printk: Rename suspend_console to console_suspend_all

Merge branch 'for-6.15-console-suspend-api-cleanup' into for-linus

2025-03-27T10:09:34Z

printk/panic: Add option to allow non-panic CPUs to write to the ring buffer.

2025-03-20T14:48:36Z

Commit 779dbc2e78d7 ("printk: Avoid non-panic CPUs writing to ringbuffer") aimed to isolate panic-related messages. However, when panic() itself malfunctions, messages from non-panic CPUs become crucial for debugging. While commit bcc954c6caba ("printk/panic: Allow cpu backtraces to be written into ringbuffer during panic") enables non-panic CPU backtraces, it may not provide sufficient diagnostic information. Introduce the "debug_non_panic_cpus" command-line option, enabling non-panic CPU messages to be stored in the ring buffer during a panic. This also prevents discarding non-finalized messages from non-panic CPUs during console flushing, providing a more comprehensive view of system state during critical failures. Link: https://lore.kernel.org/all/Z8cLEkqLL2IOyNIj@pathway/ Signed-off-by: Donghyeok Choe Reviewed-by: Petr Mladek Link: https://lore.kernel.org/r/20250318022320.2428155-1-d7271.choe@samsung.com [pmladek@suse.com: Added documentation, added module_parameter, removed printk_ prefix.] Tested-by: Petr Mladek Signed-off-by: Petr Mladek

printk: Add an option to allow ttynull to be a default console device

2025-03-17T15:25:18Z

The new option is CONFIG_NULL_TTY_DEFAULT_CONSOLE. if enabled, and CONFIG_VT is disabled, ttynull will become the default primary console device. ttynull will be the only console device usually with this option enabled. Some architectures do call add_preferred_console() which may add another console though. Motivation: Many distributions ship with CONFIG_VT enabled. On tested desktop hardware if CONFIG_VT is disabled, the default console device falls back to /dev/ttyS0 instead of /dev/tty. This could cause issues in user space, and hardware problems: 1. The user space issues include the case where /dev/ttyS0 is disconnected, and the TCGETS ioctl, which some user space libraries use as a probe to determine if a file is a tty, is called on /dev/console and fails. Programs that call isatty() on /dev/console and get an incorrect false value may skip expected logging to /dev/console. 2. The hardware issues include the case if a user has a science instrument or other device connected to the /dev/ttyS0 port, and they were to upgrade to a kernel that is disabling the CONFIG_VT option, kernel logs will then be sent to the device connected to /dev/ttyS0 unless they edit their kernel command line manually. The new CONFIG_NULL_TTY_DEFAULT_CONSOLE option will give users and distribution maintainers an option to avoid this. Disabling CONFIG_VT and enabling CONFIG_NULL_TTY_DEFAULT_CONSOLE will ensure the default kernel console behavior is not dependent on hardware configuration by default, and avoid unexpected new behavior on devices connected to the /dev/ttyS0 serial port. Reviewed-by: Petr Mladek Tested-by: Petr Mladek Signed-off-by: Adam Simonelli Link: https://lore.kernel.org/r/20250314160749.3286153-2-adamsimonelli@gmail.com [pmladek@suse.com: Fixed indentation of the commit message.] Signed-off-by: Petr Mladek

printk: Check CON_SUSPEND when unblanking a console

2025-03-11T11:52:15Z

The commit 9e70a5e109a4 ("printk: Add per-console suspended state") introduced the CON_SUSPENDED flag for consoles. The suspended consoles will stop receiving messages, so don't unblank suspended consoles because it won't be showing anything either way. Signed-off-by: Marcos Paulo de Souza Reviewed-by: Petr Mladek Reviewed-by: John Ogness Link: https://lore.kernel.org/r/20250226-printk-renaming-v1-5-0b878577f2e6@suse.com Signed-off-by: Petr Mladek

printk: Rename console_start to console_resume

2025-03-11T11:51:21Z

The intent of console_start was to resume a previously suspended console, so rename it accordingly. Signed-off-by: Marcos Paulo de Souza Reviewed-by: Petr Mladek Reviewed-by: John Ogness Link: https://lore.kernel.org/r/20250226-printk-renaming-v1-4-0b878577f2e6@suse.com [pmladek@suse.com: Fixed typo in the commit message. Updated also new drm_log.c.] Signed-off-by: Petr Mladek

printk: Rename console_stop to console_suspend

2025-03-11T11:41:55Z

The intent of console_stop was in fact to suspend it, so rename the function accordingly. Signed-off-by: Marcos Paulo de Souza Reviewed-by: Petr Mladek Reviewed-by: John Ogness Link: https://lore.kernel.org/r/20250226-printk-renaming-v1-3-0b878577f2e6@suse.com [pmladek@suse.com: Fixed typo in the commit message. Updated also new drm_log.c] Signed-off-by: Petr Mladek

printk: Rename resume_console to console_resume_all

2025-03-11T10:51:27Z

The function resume_console has a misleading name, since it resumes all consoles, so rename it accordingly. Signed-off-by: Marcos Paulo de Souza Reviewed-by: Petr Mladek Reviewed-by: John Ogness Link: https://lore.kernel.org/r/20250226-printk-renaming-v1-2-0b878577f2e6@suse.com [pmladek@suse.com: Fixed typo in the commit message.] Signed-off-by: Petr Mladek

printk: Rename suspend_console to console_suspend_all

2025-03-11T10:49:34Z

The function suspend_console has a misleading name, since it suspends all consoles, so rename it accordingly. Signed-off-by: Marcos Paulo de Souza Reviewed-by: Petr Mladek Reviewed-by: John Ogness Link: https://lore.kernel.org/r/20250226-printk-renaming-v1-1-0b878577f2e6@suse.com [pmladek@suse.com: Fixed typo in the commit message.] Signed-off-by: Petr Mladek