linux-kernel - Re: [RFC PATCH v v2 0/4] avoid the extra atomic on a ref when closing a fd

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Message-ID: <CAGudoHEqJggeQGSzXAFrQKdgh3tCzo47B_hCjSznw=w-5YUXuA@mail.gmail.com>
Date: Wed, 5 Mar 2025 13:43:59 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: David Laight <david.laight.linux@...il.com>
Cc: brauner@...nel.org, viro@...iv.linux.org.uk, jack@...e.cz, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH v v2 0/4] avoid the extra atomic on a ref when closing
 a fd

On Wed, Mar 5, 2025 at 3:19 AM David Laight
<david.laight.linux@...il.com> wrote:
> Have you looked at the problem caused by epoll() ?
> The epoll code has a 'hidden' extra reference to the fd.
> This doesn't usualy matter, but some of the driver callbacks add and
> remove an extra reference - which doesn't work well if fput() has
> just decremented it to zero.
>
> The fput code might need to do a 'decrement not one' so that the
> epoll tidyup can be done while the refcount is still one.
>
> That would save the extra atomic pair that (IIRC) got added into
> the epoll callback code.
>
> Thoughts?

I am not aware of this problem and don't have particular interest in
looking at it either, sorry.

Good thing you are free to make the case to Christian. :)
-- 
Mateusz Guzik <mjguzik gmail.com>