linux-kernel - Re: BUG: spinlock trylock failure on UP, i.MX28 3.12.15-rt25

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Message-ID: <20140422094657.5b6ca1e2@gandalf.local.home>
Date:	Tue, 22 Apr 2014 09:46:57 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Stanislav Meduna <stano@...una.org>,
	"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
	Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: BUG: spinlock trylock failure on UP, i.MX28 3.12.15-rt25

[ added Peter ]

On Tue, 22 Apr 2014 13:54:39 +0200
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:
 
> this is, erm, harmless. We grab the timer lock via trylock in hardirq
> context. If the lock is already taken then we fail to get it we go for
> plan B. According to lockdep a trylock should not fail on UP. This is
> true in general except for this timer case. I was thinking abour
> disabling this lockdep check…

trylock not failing on UP, can that be an issue? I mean, if a hardirq
does a trylock to see if it can grab a lock that is not protected by
disabling irqs, and will go to plan B if it fails, on UP, it will
always get it.  But the issue is still there. That would mean that a
hardirq could have preempted a critical section and doing a trylock
here would succeed when it really should have failed.

-- Steve
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