linux-kernel - Re: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference

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Message-ID: <20100420132839.GB2628@linux.vnet.ibm.com>
Date:	Tue, 20 Apr 2010 06:28:39 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Eric Paris <eparis@...hat.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Miles Lane <miles.lane@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] RCU: don't turn off lockdep when find suspicious
 rcu_dereference_check() usage

On Tue, Apr 20, 2010 at 08:31:56AM -0400, Eric Paris wrote:
> On Tue, 2010-04-20 at 16:23 +0800, Lai Jiangshan wrote:
> 
> > [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage
> > 
> > When suspicious rcu_dereference_check() usage is detected, lockdep is still
> > available actually, so we should not call debug_locks_off() in
> > lockdep_rcu_dereference().
> > 
> > For get rid of too much "suspicious rcu_dereference_check() usage"
> > output when the "if(!debug_locks_off())" statement is removed. This patch uses
> > static variable '__warned's for very usage of "rcu_dereference*()".
> > 
> > One variable per usage, so, Now, we can get multiple complaint
> > when we detect multiple different suspicious rcu_dereference_check() usage.
> > 
> > Requested-by: Eric Paris <eparis@...hat.com>
> > Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> 
> Although mine was a linux-next kernel and it doesn't appear that I have
> rcu_dereference_protected() at all, so I dropped that bit of the patch,
> it worked great!  I got 4 more complaints to harass people with.  Feel
> free to add my tested by if you care to.
> 
> Tested-by: Eric Paris <eparis@...hat.com>

Very nice!!!  Queued for urgent, thank you Lai and Eric!!!

							Thanx, Paul
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