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

[David Rheinsberg]

Hi

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

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