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

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Message-ID: <20230531015748.GB1648@quark.localdomain>
Date:   Tue, 30 May 2023 18:57:48 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Benjamin Segall <bsegall@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH RESEND] epoll: ep_autoremove_wake_function should use
 list_del_init_careful

On Tue, May 30, 2023 at 11:32:28AM -0700, Benjamin Segall wrote:
> autoremove_wake_function uses list_del_init_careful, so should epoll's
> more aggressive variant. It only doesn't because it was copied from an
> older wait.c rather than the most recent.
> 
> Fixes: a16ceb139610 ("epoll: autoremove wakers even more aggressively")
> Signed-off-by: Ben Segall <bsegall@...gle.com>
> Cc: stable@...r.kernel.org
> ---
>  fs/eventpoll.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 52954d4637b5..081df056398a 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -1756,11 +1756,11 @@ static struct timespec64 *ep_timeout_to_timespec(struct timespec64 *to, long ms)
>  static int ep_autoremove_wake_function(struct wait_queue_entry *wq_entry,
>  				       unsigned int mode, int sync, void *key)
>  {
>  	int ret = default_wake_function(wq_entry, mode, sync, key);
>  
> -	list_del_init(&wq_entry->entry);
> +	list_del_init_careful(&wq_entry->entry);
>  	return ret;
>  }

Can you please provide a more detailed explanation about why
list_del_init_careful() is needed here?

- Eric