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

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