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Subject: Re: [PATCH 1/2 v2] WARN_ON_SMP(): Allow use in if statements on UP
From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Lai Jiangshan <laijs@cn.fujitsu.com>,
        Darren Hart <dvhart@linux.intel.com>
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Date: Fri, 18 Mar 2011 08:14:33 -0400
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On Fri, 2011-03-18 at 10:12 +0100, Peter Zijlstra wrote:
> On Thu, 2011-03-17 at 17:56 -0400, Steven Rostedt wrote:
> > + * WARN_ON(!spin_is_locked(&lock)) checks, as spin_is_locked()
> > + * returns 0 for uniprocessor settings. 
> 
> Arguably most spin_is_locked() usages should be removed in favour of
> something like lockdep_assert_held().
> 
> The latter only emits code then built with lockdep enabled and it checks
> we are indeed the owner, not some random other cpu.
> 

Perhaps we should have lockdep_assert_held() also be in
"spin_is_locked()". The warning with spin_is_locked() is still nice to
have because it can trigger on production systems that might find a code
path that it's not locked. lockdep is too heavy to run on production
systems. But if lockdep is enabled, the spin_is_locked() should probably
check ownership too.

-- Steve