linux-kernel - Re: [PATCH v5.5 10/10] mmap locking API: rename mmap_sem to mmap

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Message-ID: <20200519131009.GD189720@google.com>
Date:   Tue, 19 May 2020 06:10:09 -0700
From:   Michel Lespinasse <walken@...gle.com>
To:     Laurent Dufour <ldufour@...ux.ibm.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Liam Howlett <Liam.Howlett@...cle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        David Rientjes <rientjes@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, Ying Han <yinghan@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Daniel Jordan <daniel.m.jordan@...cle.com>
Subject: Re: [PATCH v5.5 10/10] mmap locking API: rename mmap_sem to mmap_lock

On Mon, May 18, 2020 at 03:45:22PM +0200, Laurent Dufour wrote:
> Le 24/04/2020 à 03:39, Michel Lespinasse a écrit :
> > Rename the mmap_sem field to mmap_lock. Any new uses of this lock
> > should now go through the new mmap locking api. The mmap_lock is
> > still implemented as a rwsem, though this could change in the future.
> > 
> > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > index dc9ef302f517..701f3995f621 100644
> > --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > @@ -661,7 +661,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj)
> >   	struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr;
> >   	int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT;
> > -	might_lock_read(&current->mm->mmap_sem);
> > +	might_lock_read(&current->mm->mmap_lock);
> 
> Why not a mm_might_lock_read() new API to hide the mmap_lock, and add it to
> the previous patch?

I'm not sure why this is needed - we may rework the lock to be
something else than rwsem, but might_lock_read should still apply to
it and make sense ? I'm not sure what the extra API would bring...

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.