linux-kernel - Re: [PATCH v2] vfs: shave work on failed file open

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Message-ID: <CAGudoHHcSR=xUQ6XjC4b9UiDQC1ZLSU_Pon5O_er8mQbFpU6-g@mail.gmail.com>
Date:   Wed, 27 Sep 2023 23:30:09 +0200
From:   Mateusz Guzik <mjguzik@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Christian Brauner <brauner@...nel.org>, viro@...iv.linux.org.uk,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2] vfs: shave work on failed file open

On 9/27/23, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Wed, 27 Sept 2023 at 14:06, Mateusz Guzik <mjguzik@...il.com> wrote:
>>
>> I think you attached the wrong file, it has next to no changes and in
>> particular nothing for fd lookup.
>
> The fd lookup is already safe.
>
> It already does the whole "double-check the file pointer after doing
> the increment" for other reasons - namely the whole "oh, the file
> table can be re-allocated under us" thing.
>
> So the fd lookup needs rcu, but it does all the checks to make it all
> work with SLAB_TYPESAFE_BY_RCU.
>

Indeed, nice.

Sorry, I discounted the patch after not seeing anything for fd and
file_free_rcu still being there. Looked like a WIP.

I'm going to give it a spin tomorrow along with some benching.

-- 
Mateusz Guzik <mjguzik gmail.com>