kernel/drivers/tty/serial/kgdboc.c, branch 0x221E-v0.0.1-v6.19

drivers: serial: kgdboc: Drop checks for CON_ENABLED and CON_BOOT

2025-11-27T14:54:50Z

The original code tried to find a console that has CON_BOOT _or_ CON_ENABLED flag set. The flag CON_ENABLED is set to all registered consoles, so in this case this check is always true, even for the CON_BOOT consoles. The initial intent of the kgdboc_earlycon_init was to get a console early (CON_BOOT) or later on in the process (CON_ENABLED). The code was using for_each_console macro, meaning that all console structs were previously registered on the printk() machinery. At this point, any console found on for_each_console is safe for kgdboc_earlycon_init to use. Dropping the check makes the code cleaner, and avoids further confusion by future readers of the code. Signed-off-by: Marcos Paulo de Souza Reviewed-by: Petr Mladek Link: https://patch.msgid.link/20251121-printk-cleanup-part2-v2-1-57b8b78647f4@suse.com Signed-off-by: Petr Mladek

Revert "tty/serial: Add kgdb_nmi driver"

2025-02-14T09:05:43Z

This reverts commit 0c57dfcc6c1d037243c2f8fbf62eab3633326ec0. The functionality was supoosed to be used by a later patch in the series that never landed [1]. Drop it. NOTE: part of functionality was already reverted by commit 39d0be87438a ("serial: kgdb_nmi: Remove unused knock code"). Also note that this revert is not a clean revert given code changes that have happened in the meantime. It's obvious that nobody is using this code since the two exposed functions (kgdb_register_nmi_console() and kgdb_unregister_nmi_console()) are both no-ops if "arch_kgdb_ops.enable_nmi" is not defined. No architectures define it. [1] https://lore.kernel.org/lkml/1348522080-32629-9-git-send-email-anton.vorontsov@linaro.org/ Signed-off-by: Douglas Anderson Acked-by: Andy Shevchenko Link: URL [1] Link: https://lore.kernel.org/r/20250129082535.1.Ia095eac1ae357f87d23e7af2206741f5d40788f1@changeid Signed-off-by: Greg Kroah-Hartman

serial: kgdboc: Fix NMI-safety problems from keyboard reset code

2024-04-26T16:14:10Z

Currently, when kdb is compiled with keyboard support, then we will use schedule_work() to provoke reset of the keyboard status. Unfortunately schedule_work() gets called from the kgdboc post-debug-exception handler. That risks deadlock since schedule_work() is not NMI-safe and, even on platforms where the NMI is not directly used for debugging, the debug trap can have NMI-like behaviour depending on where breakpoints are placed. Fix this by using the irq work system, which is NMI-safe, to defer the call to schedule_work() to a point when it is safe to call. Reported-by: Liuye Closes: https://lore.kernel.org/all/20240228025602.3087748-1-liu.yeC@h3c.com/ Cc: stable@vger.kernel.org Reviewed-by: Douglas Anderson Acked-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20240424-kgdboc_fix_schedule_work-v2-1-50f5a490aec5@linaro.org Signed-off-by: Daniel Thompson

tty: serial: kgdboc: fix mutex locking order for configure_kgdboc()

2023-01-16T15:44:53Z

Several mutexes are taken while setting up console serial ports. In particular, the tty_port->mutex and @console_mutex are taken: serial_pnp_probe serial8250_register_8250_port uart_add_one_port (locks tty_port->mutex) uart_configure_port register_console (locks @console_mutex) In order to synchronize kgdb's tty_find_polling_driver() with register_console(), commit 6193bc90849a ("tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()") takes the @console_mutex. However, this leads to the following call chain (with locking): platform_probe kgdboc_probe configure_kgdboc (locks @console_mutex) tty_find_polling_driver uart_poll_init (locks tty_port->mutex) uart_set_options This is clearly deadlock potential due to the reverse lock ordering. Since uart_set_options() requires holding @console_mutex in order to serialize early initialization of the serial-console lock, take the @console_mutex in uart_poll_init() instead of configure_kgdboc(). Since configure_kgdboc() was using @console_mutex for safe traversal of the console list, change it to use the SRCU iterator instead. Add comments to uart_set_options() kerneldoc mentioning that it requires holding @console_mutex (aka the console_list_lock). Fixes: 6193bc90849a ("tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()") Signed-off-by: John Ogness Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek [pmladek@suse.com: Export console_srcu_read_lock_is_held() to fix build kgdboc as a module.] Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20230112161213.1434854-1-john.ogness@linutronix.de

tty: serial: kgdboc: use console_list_lock to trap exit

2022-12-02T10:25:02Z

kgdboc_earlycon_init() uses the console_lock to ensure that no consoles are unregistered until the kgdboc_earlycon is setup. The console_list_lock should be used instead because list synchronization responsibility will be removed from the console_lock in a later change. Signed-off-by: John Ogness Reviewed-by: Daniel Thompson Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-39-john.ogness@linutronix.de

tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()

2022-12-02T10:25:02Z

Calling tty_find_polling_driver() can lead to uart_set_options() being called (via the poll_init() callback of tty_operations) to configure the uart. But uart_set_options() can also be called by register_console() (via the setup() callback of console). Take the console_list_lock to synchronize against register_console() and also use it for console list traversal. This also ensures the console list cannot change until the polling console has been chosen. Signed-off-by: John Ogness Reviewed-by: Daniel Thompson Reviewed-by: Petr Mladek Reviewed-by: Douglas Anderson Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-38-john.ogness@linutronix.de

tty: serial: kgdboc: use console_list_lock for list traversal

2022-12-02T10:25:02Z

configure_kgdboc() uses the console_lock for console list iteration. Use the console_list_lock instead because list synchronization responsibility will be removed from the console_lock in a later change. The SRCU iterator could have been used here, but a later change will relocate the locking of the console_list_lock to also provide synchronization against register_console(). Note, the console_lock is still needed to serialize the device() callback with other console operations. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Reviewed-by: Douglas Anderson Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-37-john.ogness@linutronix.de

tty: serial: kgdboc: use srcu console list iterator

2022-12-02T10:25:02Z

Use srcu console list iteration for safe console list traversal. Note that this is a preparatory change for when console_lock no longer provides synchronization for the console list. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Reviewed-by: Douglas Anderson Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-36-john.ogness@linutronix.de

tty: serial: kgdboc: document console_lock usage

2022-12-02T10:25:00Z

kgdboc_earlycon_init() uses the console_lock to ensure that no consoles are unregistered until the kgdboc_earlycon is setup. This is necessary because the trapping of the exit() callback assumes that the exit() callback is not called before the trap is setup. Explicitly document this non-typical console_lock usage. Signed-off-by: John Ogness Reviewed-by: Greg Kroah-Hartman Reviewed-by: Douglas Anderson Reviewed-by: Daniel Thompson Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-9-john.ogness@linutronix.de

serial: kgdboc: Lock console list in probe function

2022-12-02T10:24:59Z

Unprotected list walks are not necessarily safe. Signed-off-by: Thomas Gleixner Signed-off-by: John Ogness Reviewed-by: Greg Kroah-Hartman Reviewed-by: Douglas Anderson Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek Reviewed-by: Daniel Thompson Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221116162152.193147-2-john.ogness@linutronix.de