On Tue, Oct 16, 2018 at 01:40:06PM +0200, Petr Mladek wrote:

On Tue 2018-10-16 09:27:19, Peter Zijlstra wrote:

quoted

Instead of this tinkering around the edges, why don't you make the main
logbuf a lockless ringbuffer and then delegate the actual printing of
that buffer to a kthread, except for earlycon, which can do synchronous
output.

In fact, there is no problem with printk log buffer. This patchset
tries to avoid deadlock caused by console-specific locks
used by console->write() methods.

By other words, we neither need printk_safe or lockless log buffer
to fix this prolem. Instead, we need either printk_deferred context
or lockless consoles.

If you have a lockless buffer and a trailing printk thread, that's
deferred.

And earlycon _should_ be lockless (yes, I know, some suck)

But if you do this deferred nonsense that's currently in printk, then
you risk never seeing the message -- the same problem I have with the
whole printk_safe thing too.

Printing _after_ the fact is horrible for robustness.