linux-kernel - Re: [PATCH 2/2] mutex: use spin_[un]lock instead of arch_spin

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Date:	Thu, 24 Jan 2013 20:03:29 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Yuanhan Liu <yuanhan.liu@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/2] mutex: use spin_[un]lock instead of
 arch_spin_[un]lock

On Thu, 2013-01-24 at 16:56 -0800, Andrew Morton wrote:
>  
> > Actually this perhaps hurts lockdep. We want to keep the
> > arch_spin_(un)lock() versions because each spin_lock() and spin_unlock()
> > needs to be verified by lockdep. Lockdep also verifies mutex locks. But
> > with this change, for every mutex, it's going to also analyze a
> > spin_lock and spin_unlock twice each (one for mutex lock and one for
> > unlock). As this is just locking the mutex internals, it may not be
> > necessary to debug it via lockdep. Hence we probably want to keep the
> > arch_* version.
> 
> In what way is this actually a problem?  lockdep will have more work to
> do (and given the frequency of mutex_lock/unlock, that overhead may be
> significant).  Anything else?

Ingo probably can answer this better than I can. I'll let him do it when
he wakes up tomorrow.

-- Steve


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