linux-kernel - Re: [PATCH net-next] net: socket: integrate sockfd_lookup() and sockfd_lookup

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Date:   Thu, 23 Sep 2021 09:49:49 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Yajun Deng <yajun.deng@...ux.dev>, davem@...emloft.net,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: socket: integrate sockfd_lookup() and
 sockfd_lookup_light()



On 9/21/21 11:31 PM, Yajun Deng wrote:
> As commit 6cb153cab92a("[NET]: use fget_light() in net/socket.c") said,
> sockfd_lookup_light() is lower load than sockfd_lookup(). So we can
> remove sockfd_lookup() but keep the name. As the same time, move flags
> to sockfd_put().

???

> 
> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> ---
>  include/linux/net.h |   8 +++-
>  net/socket.c        | 101 +++++++++++++++++---------------------------
>  2 files changed, 46 insertions(+), 63 deletions(-)
> 
> diff --git a/include/linux/net.h b/include/linux/net.h
> index ba736b457a06..63a179d4f760 100644
> --- a/include/linux/net.h
> +++ b/include/linux/net.h
> @@ -238,8 +238,14 @@ int sock_recvmsg(struct socket *sock, struct msghdr *msg, int flags);
>  struct file *sock_alloc_file(struct socket *sock, int flags, const char *dname);
>  struct socket *sockfd_lookup(int fd, int *err);
>  struct socket *sock_from_file(struct file *file);
> -#define		     sockfd_put(sock) fput(sock->file)
>  int net_ratelimit(void);
> +#define		     sockfd_put(sock)             \
> +do {                                              \
> +	struct fd *fd = (struct fd *)&sock->file; \
> +						  \
> +	if (fd->flags & FDPUT_FPUT)               \
> +		fput(sock->file);                 \
> +} while (0)
>  

Really ?

I wonder how was this tested ?

We can not store FDPUT_FPUT in the sock itself, for obvious reasons.
Each thread needs to keep this information private.