Re: [RFC 2/2] printk: Add more information about the printk caller

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

On (20/09/23 15:56), Petr Mladek wrote:
[..]
>  	/*
>  	 * To reduce unnecessarily reopening, first check if the descriptor
> -	 * state and caller ID are correct.
> +	 * state and caller infromation are correct.
>  	 */
> -	d_state = desc_read(desc_ring, id, &desc, NULL, &cid);
> -	if (d_state != desc_committed || cid != caller_id)
> +	d_state = desc_read(desc_ring, id, &desc, NULL, &cal);
> +	if (d_state != desc_committed ||
> +	    cal.pid != caller->pid ||
> +	    cal.cpu_ctx != caller->cpu_ctx) {

You probably might want to factor out ctx check into a static
inline helper. Since you use this check in several places, and
we may check more context fields in the future.

[..]
> +/* Information about the process and context that adds the message */
> +struct printk_caller {
> +	pid_t pid;	/* thread id */
> +	u32 cpu_ctx;	/* processor id and interrupt context */
> +};

A question. Suppose we have a task which does

	CPU0

	pr_err(...);

	preempt_disable();
	pr_err(...);
	preempt_enable();

	pr_err(...);

	rcu_read_lock();
	pr_info(...);
	rcu_read_unlock();

Should we distinguish those as 3 different contexts?

- normal printk
- printk under disabled preemption (affects scheduling)
- printk under RCU read side lock (affects RCU grace periods)

	-ss