linux-kernel - Re: [PATCH v2] lockdep: Let lock_is_held_type() detect recursive read as read

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Date:   Wed, 8 Sep 2021 12:17:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Waiman Long <llong@...hat.com>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] lockdep: Let lock_is_held_type() detect recursive
 read as read

On Wed, Sep 08, 2021 at 10:16:19AM +0800, Boqun Feng wrote:
> On Fri, Sep 03, 2021 at 10:40:01AM +0200, Sebastian Andrzej Siewior wrote:
> > lock_is_held_type(, 1) detects acquired read locks. It only recognized
> > locks acquired with lock_acquire_shared(). Read locks acquired with
> > lock_acquire_shared_recursive() are not recognized because a `2' is
> > stored as the read value.
> > 
> > Rework the check to additionally recognise lock's read value one and two
> > as a read held lock.
> > 
> > Fixes: e918188611f07 ("locking: More accurate annotations for read_lock()")
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> > ---
> > v1…v2:
> >   - simplify the read check to !!read as suggested by Waiman Long.
> > 
> >  kernel/locking/lockdep.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > --- a/kernel/locking/lockdep.c
> > +++ b/kernel/locking/lockdep.c
> > @@ -5366,7 +5366,7 @@ int __lock_is_held(const struct lockdep_
> >  		struct held_lock *hlock = curr->held_locks + i;
> >  
> >  		if (match_held_lock(hlock, lock)) {
> > -			if (read == -1 || hlock->read == read)
> > +			if (read == -1 || hlock->read == !!read)
> 
> I think this should be:
> 
> 	!!hlock->read == read
> 
> With that,
> 
> Acked-by: Boqun Feng <boqun.feng@...il.com>

Thanks!