Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel panic - not syncing: panic_on_warn set ..."

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

On (03/19/19 09:10), Dmitry Vyukov wrote:

[..]

> In some setups we read out output with "dmesg -w" (should stream
> output as well) in absence of a better solution. Will this be affected
> by SYSLOG_ACTION_CLEAR?

There is a small chance that syslog/devkmsg can be affected

	syslog_clear()
	{
		clear_seq = log_next_seq;
		clear_idx = log_next_idx;
	}

	syslog_print_all()
	{
		...
		seq = clear_seq;
		idx = clear_idx;
		while (seq < log_next_seq) {
		...
			len += msg_print_text(msg, true, time, NULL, 0);
		}
		...
	}

devkmsg also may be affected

	syslog_clear()
	{
		clear_seq = log_next_seq;
		clear_idx = log_next_idx;
	}

	devkmsg_llseek()
	{
	...
		case SEEK_DATA:
			user->idx = clear_idx;
			user->seq = clear_seq;
			break;
	...
	}

user->idx/user->seq then are used in devkmsg poll()/read(). syslog is
more likely to be affected, I think.

	-ss