Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 31 May 2023 15:26:35 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Benjamin Segall <bsegall@google.com>
Cc:     Christian Brauner <brauner@kernel.org>,
        Eric Biggers <ebiggers@kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH RESEND] epoll: ep_autoremove_wake_function should use
 list_del_init_careful
Message-Id: <20230531152635.e8bb796bee235977c141138c@linux-foundation.org>
In-Reply-To: <xm26ilc8uoz6.fsf@google.com>
References: <xm26pm6hvfer.fsf@google.com>
        <20230531015748.GB1648@quark.localdomain>
        <20230531-zupacken-laute-22564cd952f7@brauner>
        <xm26ilc8uoz6.fsf@google.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Precedence: bulk

On Wed, 31 May 2023 15:15:41 -0700 Benjamin Segall <bsegall@google.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.