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

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Message-ID: <20230531-zupacken-laute-22564cd952f7@brauner>
Date:   Wed, 31 May 2023 09:53:01 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Benjamin Segall <bsegall@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        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 06:57:48PM -0700, Eric Biggers wrote:
> 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?

Yeah, this needs more explanation... Next time someone looks at this
code and there's a *_careful() added they'll want to know why.