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

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Date:   Wed, 29 Jul 2020 11:03:55 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        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 (20/07/21 17:03), John Ogness wrote:
> On 2020-07-21, Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:
> >> 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()".
> 
> If bit31 is set, the upper 8 bits could specify what the lower 24 bits
> represent. That would give some freedom for the future.
> 
> For example:
> 
> 0x80 = cpu id (generic context)
> 0x81 = interrupt number
> 0x82 = cpu id (nmi context)

Looks good to me. I'd probably add in_softirq state. So the contexts
are: in_task, in_softirq, in_irq, in_nmi

For the purpose of future extensions, I would probably consider
u64 for callerid. So that we can store more "state bits" in the future,
like disabled/enabled preemption; disabled/enabled local irqs; etc.

	-ss