linux-kernel - Re: [PATCH 1/3] printk: Fix kdb_trap

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Message-ID: <20171012113439.3temezwthmrz3pbu@hirez.programming.kicks-ass.net>
Date:   Thu, 12 Oct 2017 13:34:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     sergey.senozhatsky@...il.com, linux-kernel@...r.kernel.org,
        rostedt@...dmis.org, mingo@...nel.org, tglx@...utronix.de,
        Jason Wessel <jason.wessel@...driver.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/3] printk: Fix kdb_trap_printk placement

On Thu, Oct 12, 2017 at 12:03:04PM +0200, Petr Mladek wrote:
> On Thu 2017-10-12 11:45:37, Petr Mladek wrote:
> > Hi,
> > 
> > I thought about this a lot from several angles. And I would prefer
> > sligly different placement, see the patch below.
> > 
> > On Thu 2017-09-28 14:18:24, Peter Zijlstra wrote:
> > > Some people figured vprintk_emit() makes for a nice API and exported
> > > it, bypassing the kdb trap.
> > 
> > Sigh, printk() API is pretty complicated and this export
> > made it much worse. Well, there are two things:
> > 
> > First, kdb_trap_printk name is a bit misleading. It is not a
> > generic trap of any printk message. Instead it seems to be
> > used to redirect only particular messages from some existing
> > functions, e.g. show_regs() called from kdb_dumpregs().
> > 
> > Second, it seems that the only user of the exported vprintk_emit()
> > is dev_vprintk_emit(). I believe that code using this wrapper
> > is not called in the sections where kdb_trap_printk is incremented.
> 
> Well, I wonder if we should go even further and stop exporting
> vprintk_emit(). IMHO, the only reason was dev_print_emit() and
> the ability to pass the extra "dict" parameter.

You have my blessing there, but the device folks might have an opinion
on that; Cc'ed Gregkh.

> My aim is to redirect all the exported interfaces into vprintk_func
> (need another name?) where the right implementation will be chosen
> by the context (NMI, printk_safe, kdb, deferred?, printk_early, normal).
> 
> In each case, I would like to have all these re-directions on a single
> place to make the printk() code better readable.
> 
> IMHO, it would make sense to do this clean up first before
> this patchset adds more twists. But I am afraid that we will
> meet some problems and it make take longer. I am open for
> opinions.
> 
> Best Regards,
> Petr