linux-kernel - Re: [RFC 3/3] sysrq: Warn about insufficient console

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Date:   Mon, 14 Jan 2019 17:05:22 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 3/3] sysrq: Warn about insufficient console_loglevel

On (01/11/19 17:20), Petr Mladek wrote:
> +static void warn_console(bool console_suppressed,
> +			 int orig_log_level,
> +			 struct sysrq_key_op *op_p)
> +{
> +	static int warned;
> +
> +	if (warned)
> +		return;
> +
> +	/* Do not warn when people are already setting loglevel via sysrq */
> +	if (op_p->enable_mask & SYSRQ_ENABLE_LOG) {
> +		warned = 1;
> +		return;
> +	}
> +
> +	if (console_suppressed) {
> +		pr_info("Messages filtered by console_loglevel (%d)%s\n",
> +			orig_log_level,
> +			sysrq_on_mask(SYSRQ_ENABLE_LOG) ? ", try SysRq+7" : "");
> +		warned = 1;
> +	}
> +}

I understand the intent.

Some comments:

- Not all of sysrq handlers printk() data. There are some quiet
  handlers. E.g. sysrq_handle_unraw(). Having "Messages filtered by
  console_loglevel" can be confusing.

- Not all sysrq handlers use INFO level.
  E.g. sync_inodes_sb()->WARN_ON()->pr_warn(). So once again there can
  be a "false positive" "Messages filtered" error, while in fact
  no messages would be filtered out.

What do you think?

	-ss