linux-kernel - Re: [PATCH] x86/spinlocks: Avoid a deadlock when someone unlock a zapped ticked spinlock

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Message-ID: <20151022101626.GN2508@worktop.programming.kicks-ass.net>
Date:	Thu, 22 Oct 2015 12:16:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/spinlocks: Avoid a deadlock when someone unlock a
 zapped ticked spinlock

On Thu, Oct 22, 2015 at 11:39:38AM +0200, Petr Mladek wrote:
> Maybe, we could add support to use early console in case of Oops and
> panic. But we should not do this by default. It would help, especially
> when the problem is reproducible and we get stacked with the normal
> console.

What I typically do is route everything to 8250 early console and rip
out everything printk buffer nonsense.

That gets you a fairly reliable console, no locking, only vscnprintf()
and OUTB banging.

No printk() wanting to do wakeups and other such nonsense that doesn't
work.

I appreciate that might not be for everybody, but it also shouldn't be
this hard to get something reliable.
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