linux-kernel - Re: [PATCH] lockdep: make print_lock_name() robust against non-existing lock

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Message-ID: <20150416155028.GT27490@worktop.programming.kicks-ass.net>
Date:	Thu, 16 Apr 2015 17:50:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Andreas Messerschmid <andreas@...utronix.de>
Subject: Re: [PATCH] lockdep: make print_lock_name() robust against
 non-existing lock_class

On Thu, Apr 16, 2015 at 05:39:36PM +0200, Sebastian Andrzej Siewior wrote:
> * Peter Zijlstra | 2015-04-16 17:35:03 [+0200]:
> 
> >On Thu, Apr 16, 2015 at 04:50:21PM +0200, Sebastian Andrzej Siewior wrote:
> >
> >> Andreas confirmed that it works for him on v3.18 with minor adjustment.
> >> 
> >> <---
> >> +       struct held_lock lock = READ_ONCE(*hlock);
> >> +       unsigned int class_idx = lock.class_idx;
> >> --->
> >> 
> >
> >I'm confused by the need for that. What was the failure with the
> >proposed patch?
> 
> It was tested on v3.18, there might have been a change between v3.18 &
> 4.0. The patch as-is did no compile:

Yeah, I might not have compiled it..

>  in file included from arch/x86/include/asm/current.h:4:0,
>                   from include/linux/mutex.h:13,
>                   from kernel/locking/lockdep.c:29:
>  kernel/locking/lockdep.c: In function ‘print_lock’:
>  kernel/locking/lockdep.c:558:37: error: ‘typeof’ applied to a bit-field
>    unsigned int class_idx = READ_ONCE(hlock->class_idx);

Ah! Indeed so, copying all of the hlock is overdoing it a bit but would
work I suppose.

Thanks!
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