linux-kernel - Re: [PATCH v9 11/17] mm: replace vm_lock and detached flag with a reference count

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Message-ID: <CAGudoHH6TKX8EnoK2aSSBc_4EKgOWV=bRAqreFWbEqBJL5RcKQ@mail.gmail.com>
Date: Sat, 11 Jan 2025 21:31:31 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, peterz@...radead.org, willy@...radead.org, 
	liam.howlett@...cle.com, lorenzo.stoakes@...cle.com, 
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Subject: Re: [PATCH v9 11/17] mm: replace vm_lock and detached flag with a
 reference count

On Sat, Jan 11, 2025 at 9:14 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> On Sat, Jan 11, 2025 at 3:24 AM Mateusz Guzik <mjguzik@...il.com> wrote:
> > The previous modification of this spot to raw_read_seqcount loses the
> > acquire fence, making the above comment not line up with the code.
>
> Is it? From reading the seqcount code
> (https://elixir.bootlin.com/linux/v6.13-rc3/source/include/linux/seqlock.h#L211):
>
> raw_read_seqcount()
>     seqprop_sequence()
>         __seqprop(s, sequence)
>             __seqprop_sequence()
>                 smp_load_acquire()
>
> smp_load_acquire() still provides the acquire fence. Am I missing something?
>

That's fine indeed.

In a different project there is an equivalent API which skips
barriers, too quick glance suggested this is what's going on here. My
bad, sorry for false alarm on this front. :)

-- 
Mateusz Guzik <mjguzik gmail.com>