linux-kernel - Re: [RFC PATCH RESEND 04/28] mm: move mmap

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Date:   Fri, 2 Sep 2022 10:46:20 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Kent Overstreet <kent.overstreet@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michel Lespinasse <michel@...pinasse.org>,
        Jerome Glisse <jglisse@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>,
        Davidlohr Bueso <dave@...olabs.net>,
        Matthew Wilcox <willy@...radead.org>,
        "Liam R. Howlett" <liam.howlett@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Laurent Dufour <laurent.dufour@...ibm.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Song Liu <songliubraving@...com>, Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>, dhowells@...hat.com,
        Hugh Dickins <hughd@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Minchan Kim <minchan@...gle.com>,
        kernel-team <kernel-team@...roid.com>,
        linux-mm <linux-mm@...ck.org>,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH RESEND 04/28] mm: move mmap_lock assert function definitions

On Thu, Sep 1, 2022 at 11:23 PM Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
>
> 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.

Ok, if at the end of the day there is a consensus that this redundancy
should be removed then I'll do that in a patch separate from this
series. Please note that in this patch I'm not changing these
functions in any way, just moving them.

>
> Sebastian
>
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