linux-kernel - Re: [PATCH] nbd: Move socket shutdown out of spinlock

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Message-ID: <CA+aCy1EyOYWe6AjXWQe0NeW4j0_togV9DvRB462xLYDLAE1n1Q@mail.gmail.com>
Date:	Thu, 12 May 2016 16:42:31 +0530
From:	Pranay Srivastava <pranjas@...il.com>
To:	Markus Pargmann <mpa@...gutronix.de>
Cc:	nbd-general@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] nbd: Move socket shutdown out of spinlock

Hi Markus,


On Thu, May 12, 2016 at 3:13 PM, Markus Pargmann <mpa@...gutronix.de> wrote:
> spinlocked ranges should be small and not contain calls into huge
> subfunctions. Fix my mistake and just get the pointer to the socket
> instead of doing everything with spinlock held.
>
> Reported-by: Mikulas Patocka <mikulas@...bright.com>
> Signed-off-by: Markus Pargmann <mpa@...gutronix.de>
> ---
>  drivers/block/nbd.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 0b892eed06a0..157bf3da876e 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -173,20 +173,22 @@ static void nbd_end_request(struct nbd_device *nbd, struct request *req)
>   */
>  static void sock_shutdown(struct nbd_device *nbd)
>  {
> +       struct socket *sock;
> +
>         spin_lock_irq(&nbd->sock_lock);
> +       sock = nbd->sock;
> +       nbd->sock = NULL;
> +       spin_unlock_irq(&nbd->sock_lock);
>
> -       if (!nbd->sock) {
> -               spin_unlock_irq(&nbd->sock_lock);
> +       if (!sock)
>                 return;
> -       }
> +
> +       del_timer(&nbd->timeout_timer);
>
>         dev_warn(disk_to_dev(nbd->disk), "shutting down socket\n");
> -       kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
> -       sockfd_put(nbd->sock);
> -       nbd->sock = NULL;
> -       spin_unlock_irq(&nbd->sock_lock);
> +       kernel_sock_shutdown(sock, SHUT_RDWR);
> +       sockfd_put(sock);
>
> -       del_timer(&nbd->timeout_timer);
>  }
>
>  static void nbd_xmit_timeout(unsigned long arg)

I was concerned about nbd_xmit_timeout as well. There's also a call to
kernel_sock_shutdown,
while holding the spin_lock in the timeout. The above is ok for
sock_shutdown but some kind of change
is also required in nbd_xmit_timeout as well. My patch addressed both these.

Can you have a look at that again.


> --
> 2.8.0.rc3
>



-- 
        ---P.K.S