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Date:   Tue, 9 Oct 2018 06:36:50 -0700
From:   "Paul E. McKenney" <paulmck@linux.ibm.com>
To:     Will Deacon <will.deacon@arm.com>
Cc:     Lance Roy <ldr709@gmail.com>, linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH 12/16] locking/mutex: Replace spin_is_locked() with
 lockdep
Reply-To: paulmck@linux.ibm.com
References: <20181003053902.6910-1-ldr709@gmail.com>
 <20181003053902.6910-13-ldr709@gmail.com>
 <20181009121809.GG6248@arm.com>
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On Tue, Oct 09, 2018 at 01:18:10PM +0100, Will Deacon wrote:
> On Tue, Oct 02, 2018 at 10:38:58PM -0700, Lance Roy wrote:
> > lockdep_assert_held() is better suited to checking locking requirements,
> > since it won't get confused when someone else holds the lock. This is
> > also a step towards possibly removing spin_is_locked().
> > 
> > Signed-off-by: Lance Roy <ldr709@gmail.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: Will Deacon <will.deacon@arm.com>
> > ---
> >  kernel/locking/mutex-debug.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
> > index 9aa713629387..771d4ca96dda 100644
> > --- a/kernel/locking/mutex-debug.c
> > +++ b/kernel/locking/mutex-debug.c
> > @@ -36,7 +36,7 @@ void debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
> >  
> >  void debug_mutex_wake_waiter(struct mutex *lock, struct mutex_waiter *waiter)
> >  {
> > -	SMP_DEBUG_LOCKS_WARN_ON(!spin_is_locked(&lock->wait_lock));
> > +	lockdep_assert_held(&lock->wait_lock);
> >  	DEBUG_LOCKS_WARN_ON(list_empty(&lock->wait_list));
> >  	DEBUG_LOCKS_WARN_ON(waiter->magic != waiter);
> >  	DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
> > @@ -51,7 +51,7 @@ void debug_mutex_free_waiter(struct mutex_waiter *waiter)
> >  void debug_mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
> >  			    struct task_struct *task)
> >  {
> > -	SMP_DEBUG_LOCKS_WARN_ON(!spin_is_locked(&lock->wait_lock));
> > +	lockdep_assert_held(&lock->wait_lock);
> 
> I think it's a good idea to replace debug usage of spin_is_locked() with
> calls to lockdep, but I wonder whether that means that DEBUG_MUTEXES should
> select LOCKDEP so that we don't lose coverage?
> 
> What do you think?

Makes sense to me!

But given that this was accepted into -tip, I have dropped it from my tree.

							Thanx, Paul