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

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Message-ID: <CAJuCfpHGzOdRH++=7CKqG5RHPZq82wqr+kbvHX+4-N0e4s_FJg@mail.gmail.com>
Date: Sat, 11 Jan 2025 12:58:10 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: akpm@...ux-foundation.org, peterz@...radead.org, willy@...radead.org, 
	liam.howlett@...cle.com, lorenzo.stoakes@...cle.com, 
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	linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v9 11/17] mm: replace vm_lock and detached flag with a
 reference count

On Sat, Jan 11, 2025 at 12:31 PM Mateusz Guzik <mjguzik@...il.com> wrote:
>
> 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. :)

No worries. Better to double-check than to merge a bug.
Thanks,
Suren.

>
> --
> Mateusz Guzik <mjguzik gmail.com>