Date: Tue, 29 Nov 2016 11:39:35 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>, Josh Poimboeuf <jpoimboe@redhat.com>,
        Vince Weaver <vincent.weaver@maine.edu>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        "dvyukov@google.com" <dvyukov@google.com>
Subject: Re: perf: fuzzer BUG: KASAN: stack-out-of-bounds in __unwind_start
Reply-To: paulmck@linux.vnet.ibm.com
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On Tue, Nov 29, 2016 at 06:10:38PM +0100, Peter Zijlstra wrote:
> On Tue, Nov 29, 2016 at 05:29:20PM +0100, Petr Mladek wrote:
> 
> > > > People are very busy polishing the turd we call printk, but from where
> > > > I'm sitting its terminally and unfixably broken.
> > 
> > I still hope that we could do better :-)
> 
> How? The console drivers are a complete trainwreck, you simply cannot
> build anything sensible ontop of a trainwreck.
> 
> And from what I understood from talking to someone (I again forgot who)
> at LPC, the whole reason people were poking at this is that the block
> layer (or something thereabouts) prints a gazillion lines of crap when
> you attach a stupid amount of devices (through FC or other SAN like
> things).
> 
> The way we've 'fixed' that in the scheduler (a fairly long time ago)
> when SGI complained about our printks taking too long (because they had
> 4096 CPUs), is to simply remove the printks (they're now hidden behind
> the sched_debug boot param).
> 
> 
> In any case, as long as printk has a globally serialized 'log', it, per
> design, will be worse than the console drivers its build upon. And them
> being shit precludes the entire stack from being useful.
> 
> It mostly works, most of the time, and that seems to be what Linus
> wants, since its really the best we can have given the constraints. But
> for debugging, when you have a UART, it totally blows.

UART???  They still make those things???  ;-)

							Thanx, Paul