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From: Peter Zijlstra <peterz@infradead.org>
To: David Rientjes <rientjes@google.com>
Cc: Bart Van Assche <bvanassche@acm.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"David S. Miller" <davem@davemloft.net>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3] spin_lock_nested(): Always evaluate second argument
Date: Sat, 9 Aug 2014 08:17:12 +0200	[thread overview]
Message-ID: <20140809061712.GL9918@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <alpine.DEB.2.02.1408081451470.15603@chino.kir.corp.google.com>

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On Fri, Aug 08, 2014 at 02:52:50PM -0700, David Rientjes wrote:
> On Fri, 8 Aug 2014, Bart Van Assche wrote:
> 
> > diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
> > index 3f2867f..262ba4e 100644
> > --- a/include/linux/spinlock.h
> > +++ b/include/linux/spinlock.h
> > @@ -197,7 +197,13 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
> >  		 _raw_spin_lock_nest_lock(lock, &(nest_lock)->dep_map);	\
> >  	 } while (0)
> >  #else
> > -# define raw_spin_lock_nested(lock, subclass)		_raw_spin_lock(lock)
> > +/*
> > + * Always evaluate the 'subclass' argument to avoid that the compiler
> > + * warns about set-but-not-used variables when building with
> > + * CONFIG_DEBUG_LOCK_ALLOC=n and with W=1.
> > + */
> 
> I was hoping there was going to be a more important reason for this change 
> than to avoid compiler warnings, such as an example where someone is doing 
> spin_lock_nested(lock, subclass) and the expression for "subclass" 
> requires evaluation in all configs.

That would stink, having that argument have side effects. I'd call that
a plain old bug that needs fixing.



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  reply	other threads:[~2014-08-09  6:17 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-07-22  7:17 [PATCH RESEND] spin_lock_*(): Always evaluate second argument Bart Van Assche
2014-07-22 20:37 ` Andrew Morton
2014-07-22 23:16   ` David Rientjes
2014-08-06 17:07     ` Bart Van Assche
2014-08-06 17:10       ` [PATCH v2] spin_lock_nested(): " Bart Van Assche
2014-08-06 21:56         ` David Rientjes
2014-08-08 10:32           ` Bart Van Assche
2014-08-08 10:35             ` [PATCH v3] " Bart Van Assche
2014-08-08 21:52               ` David Rientjes
2014-08-09  6:17                 ` Peter Zijlstra [this message]
2014-08-13 10:56               ` [tip:locking/core] locking/spinlocks: Always evaluate the second argument of spin_lock_nested() tip-bot for Bart Van Assche

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