netdev - Re: [PATCH RFC 2/4] net, pidfs: prepare for handing out pidfds for reaped sk->sk_peer

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Message-Id: <c4a2468b-f6b1-4549-8189-ec2f72bef45e@app.fastmail.com>
Date: Thu, 24 Apr 2025 14:44:13 +0200
From: "David Rheinsberg" <david@...dahead.eu>
To: "Christian Brauner" <brauner@...nel.org>,
 "Oleg Nesterov" <oleg@...hat.com>, "Kuniyuki Iwashima" <kuniyu@...zon.com>,
 "David S. Miller" <davem@...emloft.net>,
 "Eric Dumazet" <edumazet@...gle.com>, "Jakub Kicinski" <kuba@...nel.org>,
 "Paolo Abeni" <pabeni@...hat.com>, "Simon Horman" <horms@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 netdev@...r.kernel.org, "Jan Kara" <jack@...e.cz>,
 "Alexander Mikhalitsyn" <alexander@...alicyn.com>,
 "Luca Boccassi" <bluca@...ian.org>,
 "Lennart Poettering" <lennart@...ttering.net>,
 "Daan De Meyer" <daan.j.demeyer@...il.com>, "Mike Yuan" <me@...dnzj.com>
Subject: Re: [PATCH RFC 2/4] net, pidfs: prepare for handing out pidfds for reaped
 sk->sk_peer_pid

Hi

On Thu, Apr 24, 2025, at 2:24 PM, Christian Brauner wrote:
[...]
> Link: 
> https://lore.kernel.org/lkml/20230807085203.819772-1-david@readahead.eu 
> [1]
> Signed-off-by: Christian Brauner <brauner@...nel.org>

Very nice! Highly appreciated!

> ---
>  net/unix/af_unix.c | 90 
> +++++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 79 insertions(+), 11 deletions(-)
>
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index f78a2492826f..83b5aebf499e 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -100,6 +100,7 @@
>  #include <linux/splice.h>
>  #include <linux/string.h>
>  #include <linux/uaccess.h>
> +#include <linux/pidfs.h>
>  #include <net/af_unix.h>
>  #include <net/net_namespace.h>
>  #include <net/scm.h>
> @@ -643,6 +644,14 @@ static void unix_sock_destructor(struct sock *sk)
>  		return;
>  	}
> 
> +	if (sock_flag(sk, SOCK_RCU_FREE)) {
> +		pr_info("Attempting to release RCU protected socket with sleeping 
> locks: %p\n", sk);
> +		return;
> +	}

unix-sockets do not use `SOCK_RCU_FREE`, but even if they did, doesn't this flag imply that the destructor is delayed via `call_rcu`, and thus *IS* allowed to sleep? And then, sleeping in the destructor is always safe, isn't it? `SOCK_RCU_FREE` just guarantees that it is delayed for at least an RCU grace period, right? Not sure, what you are getting at here, but I might be missing something obvious as well.

Regardless, wouldn't you want WARN_ON_ONCE() rather than pr_info?

Otherwise looks good to me!
David