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    Subject[RFC][PATCHv2 7/8] printk: add printk emergency_mode parameter
    Date
    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 <sergey.senozhatsky@gmail.com>
    ---
    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
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