linux-kernel - Re: [PATCH RESEND] epoll: ep_autoremove_wake_function should use list_del_init

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Date:   Wed, 31 May 2023 15:26:35 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Benjamin Segall <bsegall@...gle.com>
Cc:     Christian Brauner <brauner@...nel.org>,
        Eric Biggers <ebiggers@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH RESEND] epoll: ep_autoremove_wake_function should use
 list_del_init_careful

On Wed, 31 May 2023 15:15:41 -0700 Benjamin Segall <bsegall@...gle.com> wrote:

> >> Can you please provide a more detailed explanation about why
> >> list_del_init_careful() is needed here?
> >
> > Yeah, this needs more explanation... Next time someone looks at this
> > code and there's a *_careful() added they'll want to know why.
> 
> So the general reason is the same as with autoremove_wake_function, it
> pairs with the list_entry_careful in ep_poll (which is epoll's modified
> copy of finish_wait).
> 
> I think the original actual _problem_ was a -stable issue that was fixed
> instead by doing additional backports, so this may just avoid potential
> extra loops and avoid potential compiler shenanigans from the data race.

The point is that the foo_careful() callsites should be commented, please.