Re: [RFC] printk's sync mode for ftrace_dump()

[John Ogness <john.ogness@linutronix.de>]

On 2021-10-29, Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> ftrace_dump() is used for instance by alt-sysrq-z / sysrq_ftrace_dump().
> The function itself dumps the whole trace buffer in an irq-off section so
> no need to talk about max latencies unless this is going to change.
>
> The output on the serial is more or less brief and starts with
>     "** 397774 printk messages dropped **"
> and so I do see only the end of it. Might be okay.
> Any reason not to use the sync mode + atomic console while ftrace_dump()
> is in progress?

Since latencies are not a concern, I see no reason not to use
sync+atomic.

However, it does put us into the situation of beginning to define
non-emergency scenarios where sync+atomic is used. That rabbit hole
might go quite deep. I wonder if it might be better to introduce a new
sysrq to toggle sync mode.

John