This param permits user-space to forcibly on/off printk emergency mode via /sys/module/printk/parameters/emergency_mode node.
We have annotated sections in the kernel that switch printk to emergency, but there might be places/cases when user space would want to have printk operate in emergency mode all the time. Signed-off-by: Sergey Senozhatsky <[email protected]> --- kernel/printk/printk.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 1927b5cb5cbe..0d96839bb450 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -455,7 +455,7 @@ static struct task_struct *printk_kthread __read_mostly; static atomic_t printk_emergency __read_mostly; /* * Disable printk_kthread permanently. Unlike `oops_in_progress' - * it doesn't go back to 0. + * it doesn't go back to 0 (unless enforced by user-space). */ static bool printk_kthread_disabled __read_mostly; @@ -483,6 +483,24 @@ void printk_emergency_end(void) atomic_dec(&printk_emergency); } +static int printk_kthread_disabled_set(const char *val, + const struct kernel_param *kp) +{ + return param_set_bool(val, kp); +} + +static const struct kernel_param_ops printk_kthread_disabled_ops = { + .set = printk_kthread_disabled_set, + .get = param_get_bool, +}; + +module_param_cb(emergency_mode, + &printk_kthread_disabled_ops, + &printk_kthread_disabled, + 0644); +MODULE_PARM_DESC(emergency_mode, + "don't offload message printing to printk kthread"); + /* Return log buffer address */ char *log_buf_addr_get(void) { -- 2.12.2
