linux-kernel - Re: [PATCH 3/3] mutex: Add missing annotations

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Date:   Sat, 1 Feb 2020 00:27:02 +0000 (GMT)
From:   Jules Irenge <jbi.octave@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Jules Irenge <jbi.octave@...il.com>, boqun.feng@...il.com,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mutex: Add missing annotations


Thanks for the feedback, I did not have a thorough analyse.

I just realised it. Yes, some warnings generated after are 
pointless others look genuine. Next time I will 
have a thorough analyse and test before sending. 

I apologise for this.  

I really appreciate your feedback.

Kind regards,
Jules

On Mon, 27 Jan 2020, Peter Zijlstra wrote:

> On Fri, Jan 24, 2020 at 08:12:20PM +0000, Jules Irenge wrote:
> > Sparse reports false warnings and hide real warnings
> > where mutex_lock() and mutex_unlock() are used within the kernel
> > An example is within the kernel cgroup files
> > where the below warnings are found
> > |warning: context imbalance in cgroup_lock_and_drain_offline()
> > | - wrong count at exit
> > |warning: context imbalance in cgroup_procs_write_finish()
> > |- wrong count at exit
> > |warning: context imbalance in cgroup_procs_write_start()
> > |- wrong count at exit.
> > 
> > To fix these,
> > an __acquires(lock) is added to mutex_lock() declaration
> > a __releases(lock) to mutex_unlock() declaration
> > 
> > Signed-off-by: Jules Irenge <jbi.octave@...il.com>
> > ---
> >  include/linux/mutex.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> > index aca8f36dfac9..a8ab4029913e 100644
> > --- a/include/linux/mutex.h
> > +++ b/include/linux/mutex.h
> > @@ -162,7 +162,7 @@ do {									\
> >  } while (0)
> >  
> >  #else
> > -extern void mutex_lock(struct mutex *lock);
> > +extern void mutex_lock(struct mutex *lock) __acquires(lock);
> >  extern int __must_check mutex_lock_interruptible(struct mutex *lock);
> >  extern int __must_check mutex_lock_killable(struct mutex *lock);
> >  extern void mutex_lock_io(struct mutex *lock);
> > @@ -181,7 +181,7 @@ extern void mutex_lock_io(struct mutex *lock);
> >   * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
> >   */
> >  extern int mutex_trylock(struct mutex *lock);
> > -extern void mutex_unlock(struct mutex *lock);
> > +extern void mutex_unlock(struct mutex *lock) __releases(lock);
> >  
> >  extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
> 
> *groan*, I despise these sparse things.
> 
> The proposed patch only annotates a tiny part of the mutex interface,
> and will thereby generate a flood of new (pointless) warnings. Worse,
> annotating them all properly will require that __cond_lock() trainwreck.
> 
>