Re: [PATCH] kernel/watchdog: flush all printk nmi buffers when hardlockup detected

[Steven Rostedt]

On Wed, 12 Feb 2020 12:04:03 +0900
Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> wrote:

> Oh, yes, ftrace printks a lot. But I sort of forgot why don't we do
> the same for "regular" NMIs. So NMIs use per-cpu buffers, expect for
> NMIs which involve ftrace dump. I'm missing something here.

Well, ftrace_dump() is called from NMI context when the system is about
to crash (ftrace_dump_on_oops). And at that moment, we care more about
the trace than other output (it's most like to contain the information
that caused the bug).

But for things like sysrq-l, that does a printk in NMI context for
normal operations, we don't want strange races to occur and affect
other printk operations. Having them in buffers controls the output a
bit better.

But with the new printk ring buffer work, perhaps that's no longer
necessary.

-- Steve