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Date:   Fri, 2 Sep 2022 08:23:46 +0200
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Kent Overstreet <kent.overstreet@linux.dev>
Cc:     Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org,
        michel@lespinasse.org, jglisse@google.com, mhocko@suse.com,
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Subject: Re: [RFC PATCH RESEND 04/28] mm: move mmap_lock assert function
 definitions
Message-ID: <YxGhcnKyV7KCiWCJ@linutronix.de>
References: <20220901173516.702122-1-surenb@google.com>
 <20220901173516.702122-5-surenb@google.com>
 <20220901202409.e2fqegqghlijkzey@moria.home.lan>
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On 2022-09-01 16:24:09 [-0400], Kent Overstreet wrote:
> > --- a/include/linux/mmap_lock.h
> > +++ b/include/linux/mmap_lock.h
> > @@ -60,6 +60,18 @@ static inline void __mmap_lock_trace_released(struct mm_struct *mm, bool write)
> >  
> >  #endif /* CONFIG_TRACING */
> >  
> > +static inline void mmap_assert_locked(struct mm_struct *mm)
> > +{
> > +	lockdep_assert_held(&mm->mmap_lock);
> > +	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
> 
> These look redundant to me - maybe there's a reason the VM developers want both,
> but I would drop the VM_BUG_ON() and just keep the lockdep_assert_held(), since
> that's the standard way to write that assertion.

Exactly. rwsem_is_locked() returns true only if the lock is "locked" not
necessary by the caller. lockdep_assert_held() checks that the lock is
locked by the caller - this is the important part.

Sebastian