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

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Message-ID: <Y8e6lm76fIoT0603@dhcp22.suse.cz>
Date:   Wed, 18 Jan 2023 10:23:34 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
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Subject: Re: [PATCH 17/41] mm/mmap: move VMA locking before
 anon_vma_lock_write call

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 ....

Withtout that additional reasonaning it is not really clear why that is
needed and seems arbitrary.

-- 
Michal Hocko
SUSE Labs