linux-kernel - Re: [PATCH 2/4] printk: store instead of processing cont parts

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Date:   Tue, 21 Jul 2020 23:42:20 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kexec@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] printk: store instead of processing cont parts

On (20/07/20 11:30), Linus Torvalds wrote:
> > Do I get it right, what you are saying is - when we process a PR_CONT
> > message the cont buffer should already contain previous non-LOG_NEWLINE
> > and non-PR_CONT message, otherwise it's a bug?
> 
> No.
> 
> I'm saying that the code that does PR_CONT should have done *some*
> printing before, otherwise it's at the very least questionable.
> 
> IOW, you can't just randomly start printing with PR_CONT, without
> having established _some_ context for it.

OK, I see. I sort of suspect that we may actually have code that does
just pr_cont() (e.g. what Joe pointed out). It doesn't seem like that
"establish a context" was ever enforced, doing a bunch of pr_cont()
simply works.

[..]
> That said, we have traditionally used not just "current process", but
> also "last irq-level" as the context information, so I do think it
> would be good to continue to do that.

OK, so basically, extending printk_caller_id() so that for IRQ/NMI
we will have more info than just "0x80000000 + raw_smp_processor_id()".

	-ss