[ added Peter ]

On Tue, 22 Apr 2014 13:54:39 +0200
Sebastian Andrzej Siewior [off-list ref] 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