From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC][PATCHv2 2/4] printk: move printk_safe macros to printk
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Date: Wed, 17 Oct 2018 09:57:28 +0200
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To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com>, Steven Rostedt <rostedt@goodmis.org>, Daniel Wang <wonderfly@google.com>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Alan Cox <gnomes@lxorguk.ukuu.org.uk>, Jiri Slaby <jslaby@suse.com>, Peter Feiner <pfeiner@google.com>, linux-serial@vger.kernel.org, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
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On Wed, Oct 17, 2018 at 01:32:51PM +0900, Sergey Senozhatsky wrote:
> This probably will be a bit more hairy. logbuf is written to by many
> sources and is read from by many sides, including user-space [both read()
> and write()]. So we will need more flags/magic around memcpy(). A simple,
> "grab the logbuf entry, set the proper offset to point to the next available
> logbuf record and then do memcpy()" won't suffice. We need a flag for
> "memcpy() complete, we can read this entry". Otherwise:

Sure, but lockless buffers mostly have reserve and commit stages anyway.
Exactly to avoid that problem.

> All right. OK. So we are on the same page here:

> - Have more opinions on this. People please speak out.
> - Have clear "let's do it" from Cc-ed people.
> 
> 
> If we are really doing this, then let's split it and have
> incremental changes. Namely, what I suggest is:

I'd start by replacing logbuf with the lockless buffer and ripping out
the current nmi/safe/etc.. bollocks.

There is absolutely no point what so ever in doing anything until that
is sorted.

After that, move the console output to a kthread, but keep earlycon (if
set) synchronous.

Also avoid the whole panic/warn special case when earlycon is set, no
point in doing dodgy crap when you know you have a good option already.