linux-kernel - Re: [PATCH 17/41] mm/mmap: move VMA locking before anon_vma_lock

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Message-ID: <Y8hls4MH353ZnlQu@dhcp22.suse.cz>
Date:   Wed, 18 Jan 2023 22:33:39 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, michel@...pinasse.org,
        jglisse@...gle.com, vbabka@...e.cz, hannes@...xchg.org,
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Subject: Re: [PATCH 17/41] mm/mmap: move VMA locking before
 anon_vma_lock_write call

On Wed 18-01-23 10:09:29, Suren Baghdasaryan wrote:
> On Wed, Jan 18, 2023 at 1:23 AM Michal Hocko <mhocko@...e.com> wrote:
> >
> > On Tue 17-01-23 18:01:01, Suren Baghdasaryan wrote:
> > > On Tue, Jan 17, 2023 at 7:16 AM Michal Hocko <mhocko@...e.com> wrote:
> > > >
> > > > On Mon 09-01-23 12:53:12, Suren Baghdasaryan wrote:
> > > > > Move VMA flag modification (which now implies VMA locking) before
> > > > > anon_vma_lock_write to match the locking order of page fault handler.
> > > >
> > > > Does this changelog assumes per vma locking in the #PF?
> > >
> > > Hmm, you are right. Page fault handlers do not use per-vma locks yet
> > > but the changelog already talks about that. Maybe I should change it
> > > to simply:
> > > ```
> > > Move VMA flag modification (which now implies VMA locking) before
> > > vma_adjust_trans_huge() to ensure the modifications are done after VMA
> > > has been locked.
> >
> > Because ....
> 
> because vma_adjust_trans_huge() modifies the VMA and such
> modifications should be done under VMA write-lock protection.

So it will become:
Move VMA flag modification (which now implies VMA locking) before
vma_adjust_trans_huge() to ensure the modifications are done after VMA
has been locked. Because vma_adjust_trans_huge() modifies the VMA and such
modifications should be done under VMA write-lock protection.

which is effectivelly saying
vma_adjust_trans_huge() modifies the VMA and such modifications should
be done under VMA write-lock protection so move VMA flag modifications
before so all of them are covered by the same write protection.

right?
-- 
Michal Hocko
SUSE Labs