Re: [RFC PATCH RESEND 04/28] mm: move mmap_lock assert function definitions

From: Suren Baghdasaryan <surenb@google.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Michel Lespinasse <michel@lespinasse.org>,
	Joel Fernandes <joelaf@google.com>,
	Song Liu <songliubraving@fb.com>, Michal Hocko <mhocko@suse.com>,
	David Hildenbrand <david@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Peter Xu <peterx@redhat.com>,
	dhowells@redhat.com, linux-mm <linux-mm@kvack.org>,
	Jerome Glisse <jglisse@google.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Minchan Kim <minchan@google.com>,
	x86@kernel.org, Hugh Dickins <hughd@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	Laurent Dufour <laurent.dufour@fr.ibm.com>,
	Mel Gorman <mgorman@suse.de>,
	David Rientjes <rientjes@google.com>,
	Axel Rasmussen <axelrasmussen@google.com>,
	kernel-team <kernel-team@android.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	"Liam R. Howlett" <liam.howlett@oracle.com>,
	Andy Lutomirski <luto@kernel.org>,
	Laurent Dufour <ldufour@linux.ibm.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-arm-kernel@lists.infradead.org,
	Kent Overstreet <kent.overstreet@linux.dev>,
	LKML <linux-kernel@vger .kernel.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [RFC PATCH RESEND 04/28] mm: move mmap_lock assert function definitions
Date: Fri, 2 Sep 2022 10:46:20 -0700	[thread overview]
Message-ID: <CAJuCfpGsOwe39Hm65VVp0Z-12e2f0wrSjvOQDhQx0XnYpr4Cbw@mail.gmail.com> (raw)
In-Reply-To: <YxGhcnKyV7KCiWCJ@linutronix.de>

On Thu, Sep 1, 2022 at 11:23 PM Sebastian Andrzej Siewior
<bigeasy@linutronix.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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