diff options
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 8 | ||||
| -rw-r--r-- | Documentation/admin-guide/serial-console.rst | 4 | ||||
| -rw-r--r-- | drivers/tty/Kconfig | 19 | ||||
| -rw-r--r-- | kernel/printk/internal.h | 1 | ||||
| -rw-r--r-- | kernel/printk/printk.c | 25 | ||||
| -rw-r--r-- | kernel/printk/printk_ringbuffer.c | 13 |
6 files changed, 62 insertions, 8 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 393563048ab5..7855bf0ab5b3 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5013,6 +5013,14 @@ Format: <bool> default: 0 (auto_verbose is enabled) + printk.debug_non_panic_cpus= + Allows storing messages from non-panic CPUs into + the printk log buffer during panic(). They are + flushed to consoles by the panic-CPU on + a best-effort basis. + Format: <bool> (1/Y/y=enable, 0/N/n=disable) + Default: disabled + printk.devkmsg={on,off,ratelimit} Control writing to /dev/kmsg. on - unlimited logging to /dev/kmsg from userspace diff --git a/Documentation/admin-guide/serial-console.rst b/Documentation/admin-guide/serial-console.rst index a3dfc2c66e01..1609e7479249 100644 --- a/Documentation/admin-guide/serial-console.rst +++ b/Documentation/admin-guide/serial-console.rst @@ -78,7 +78,9 @@ If no console device is specified, the first device found capable of acting as a system console will be used. At this time, the system first looks for a VGA card and then for a serial port. So if you don't have a VGA card in your system the first serial port will automatically -become the console. +become the console, unless the kernel is configured with the +CONFIG_NULL_TTY_DEFAULT_CONSOLE option, then it will default to using the +ttynull device. You will need to create a new device to use ``/dev/console``. The official ``/dev/console`` is now character device 5,1. diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig index 63a494d36a1f..7fb81bbaee60 100644 --- a/drivers/tty/Kconfig +++ b/drivers/tty/Kconfig @@ -383,7 +383,24 @@ config NULL_TTY available or desired. In order to use this driver, you should redirect the console to this - TTY, or boot the kernel with console=ttynull. + TTY, boot the kernel with console=ttynull, or enable + NULL_TTY_DEFAULT_CONSOLE. + + If unsure, say N. + +config NULL_TTY_DEFAULT_CONSOLE + bool "Support for console on ttynull" + depends on NULL_TTY=y && !VT_CONSOLE + help + Say Y here if you want the NULL TTY to be used as a /dev/console + device by default. + + For example, it might be useful to prevent a VT-less kernel from + writing the system log to a random device connected to the serial + port. + + Another console driver still might get preferred via the command + line, SPCR, or the device tree. If unsure, say N. diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index a91bdf802967..48a24e7b309d 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -64,6 +64,7 @@ struct dev_printk_info; extern struct printk_ringbuffer *prb; extern bool printk_kthreads_running; +extern bool debug_non_panic_cpus; __printf(4, 0) int vprintk_store(int facility, int level, diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 0e6db80d5513..1cfc943af62c 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2375,6 +2375,22 @@ void printk_legacy_allow_panic_sync(void) } } +bool __read_mostly debug_non_panic_cpus; + +#ifdef CONFIG_PRINTK_CALLER +static int __init debug_non_panic_cpus_setup(char *str) +{ + debug_non_panic_cpus = true; + pr_info("allow messages from non-panic CPUs in panic()\n"); + + return 0; +} +early_param("debug_non_panic_cpus", debug_non_panic_cpus_setup); +module_param(debug_non_panic_cpus, bool, 0644); +MODULE_PARM_DESC(debug_non_panic_cpus, + "allow messages from non-panic CPUs in panic()"); +#endif + asmlinkage int vprintk_emit(int facility, int level, const struct dev_printk_info *dev_info, const char *fmt, va_list args) @@ -2391,7 +2407,9 @@ asmlinkage int vprintk_emit(int facility, int level, * non-panic CPUs are generating any messages, they will be * silently dropped. */ - if (other_cpu_in_panic() && !panic_triggering_all_cpu_backtrace) + if (other_cpu_in_panic() && + !debug_non_panic_cpus && + !panic_triggering_all_cpu_backtrace) return 0; printk_get_console_flush_type(&ft); @@ -4287,6 +4305,11 @@ void __init console_init(void) initcall_t call; initcall_entry_t *ce; +#ifdef CONFIG_NULL_TTY_DEFAULT_CONSOLE + if (!console_set_on_cmdline) + add_preferred_console("ttynull", 0, NULL); +#endif + /* Setup the default TTY line discipline. */ n_tty_init(); diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c index 88e8f3a61922..d9fb053cff67 100644 --- a/kernel/printk/printk_ringbuffer.c +++ b/kernel/printk/printk_ringbuffer.c @@ -2133,9 +2133,9 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq, * there may be other finalized records beyond that * need to be printed for a panic situation. If this * is the panic CPU, skip this - * non-existent/non-finalized record unless it is - * at or beyond the head, in which case it is not - * possible to continue. + * non-existent/non-finalized record unless non-panic + * CPUs are still running and their debugging is + * explicitly enabled. * * Note that new messages printed on panic CPU are * finalized when we are here. The only exception @@ -2143,10 +2143,13 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq, * But it would have the sequence number returned * by "prb_next_reserve_seq() - 1". */ - if (this_cpu_in_panic() && ((*seq + 1) < prb_next_reserve_seq(rb))) + if (this_cpu_in_panic() && + (!debug_non_panic_cpus || legacy_allow_panic_sync) && + ((*seq + 1) < prb_next_reserve_seq(rb))) { (*seq)++; - else + } else { return false; + } } } |