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Re: [PATCH v4 2/5]nbd: fix might_sleep warning on socket shutdown

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Hi,

On 2016 M06 30, Thu 14:02:02 CEST Pranay Kr. Srivastava 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@twibright.com>
> Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
> 
> Changelog:
> Pranay Kr. Srivastava<pranjas@gmail.com>:
> 
> 1) Use spin_lock instead of irq version for sock_shutdown.
> 
> 2) Use system work queue to actually trigger the shutdown of
> socket. This solves the issue when kernel_sendmsg is currently
> blocked while a timeout occurs.
> 
> Signed-off-by: Pranay Kr. Srivastava <pranjas@gmail.com>
> ---
>  drivers/block/nbd.c | 57
> +++++++++++++++++++++++++++++++++-------------------- 1 file changed, 36
> insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 766c401..e362d44 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -39,6 +39,7 @@
>  #include <asm/types.h>
> 
>  #include <linux/nbd.h>
> +#include <linux/workqueue.h>
> 
>  struct nbd_device {
>  	u32 flags;
> @@ -69,6 +70,8 @@ struct nbd_device {
>  #if IS_ENABLED(CONFIG_DEBUG_FS)
>  	struct dentry *dbg_dir;
>  #endif
> +	/* This is specifically for calling sock_shutdown, for now. */
> +	struct work_struct ws_shutdown;
>  };
> 
>  #if IS_ENABLED(CONFIG_DEBUG_FS)
> @@ -95,6 +98,8 @@ static int max_part;
>   */
>  static DEFINE_SPINLOCK(nbd_lock);
> 
> +static void nbd_ws_func_shutdown(struct work_struct *);
> +

are you reading all the comments I had?...

At least respond to my comments if you disagree. I still can't see the benefit
of a function signature here if we can avoid it.

>  static inline struct device *nbd_to_dev(struct nbd_device *nbd)
>  {
>  	return disk_to_dev(nbd->disk);
> @@ -172,39 +177,36 @@ static void nbd_end_request(struct nbd_device *nbd,
> struct request *req) */
>  static void sock_shutdown(struct nbd_device *nbd)
>  {
> -	spin_lock_irq(&nbd->sock_lock);
> -
> -	if (!nbd->sock) {
> -		spin_unlock_irq(&nbd->sock_lock);
> -		return;
> -	}
> +	struct socket *sock;
> 
> -	dev_warn(disk_to_dev(nbd->disk), "shutting down socket\n");
> -	kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
> -	sockfd_put(nbd->sock);
> +	spin_lock(&nbd->sock_lock);
> +	sock = nbd->sock;
>  	nbd->sock = NULL;
> -	spin_unlock_irq(&nbd->sock_lock);
> +	spin_unlock(&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(sock, SHUT_RDWR);
> +	sockfd_put(sock);
>  }
> 
>  static void nbd_xmit_timeout(unsigned long arg)
>  {
>  	struct nbd_device *nbd = (struct nbd_device *)arg;
> -	unsigned long flags;
> 
>  	if (list_empty(&nbd->queue_head))
>  		return;
> 
> -	spin_lock_irqsave(&nbd->sock_lock, flags);
> -
>  	nbd->timedout = true;
> -
> -	if (nbd->sock)
> -		kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
> -
> -	spin_unlock_irqrestore(&nbd->sock_lock, flags);
> -
> +	/*
> +	 * Make sure sender thread sees nbd->timedout.
> +	 */
> +	smp_wmb();
> +	schedule_work(&nbd->ws_shutdown);
> +	wake_up(&nbd->waiting_wq);
>  	dev_err(nbd_to_dev(nbd), "Connection timed out, shutting down
> connection\n"); }
> 
> @@ -588,7 +590,11 @@ static int nbd_thread_send(void *data)
>  		spin_unlock_irq(&nbd->queue_lock);
> 
>  		/* handle request */
> -		nbd_handle_req(nbd, req);
> +		if (nbd->timedout) {
> +			req->errors++;
> +			nbd_end_request(nbd, req);
> +		} else
> +			nbd_handle_req(nbd, req);

I already commented on this in the last patch. This is unrelated to the patch.
If you disagree then please tell me why instead of sending the same thing
again.

Also brackets on the else part would be preferred.

Regards,

Markus

>  	}
> 
>  	nbd->task_send = NULL;
> @@ -663,6 +669,7 @@ static void nbd_reset(struct nbd_device *nbd)
>  	set_capacity(nbd->disk, 0);
>  	nbd->flags = 0;
>  	nbd->xmit_timeout = 0;
> +	INIT_WORK(&nbd->ws_shutdown, nbd_ws_func_shutdown);
>  	queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
>  	del_timer_sync(&nbd->timeout_timer);
>  }
> @@ -797,11 +804,11 @@ static int __nbd_ioctl(struct block_device *bdev,
> struct nbd_device *nbd, error = nbd_thread_recv(nbd, bdev);
>  		nbd_dev_dbg_close(nbd);
>  		kthread_stop(thread);
> +		sock_shutdown(nbd);
> 
>  		mutex_lock(&nbd->tx_lock);
>  		nbd->task_recv = NULL;
> 
> -		sock_shutdown(nbd);
>  		nbd_clear_que(nbd);
>  		kill_bdev(bdev);
>  		nbd_bdev_reset(bdev);
> @@ -857,6 +864,14 @@ static const struct block_device_operations nbd_fops =
> { .compat_ioctl =	nbd_ioctl,
>  };
> 
> +static void nbd_ws_func_shutdown(struct work_struct *ws_nbd)
> +{
> +	struct nbd_device *nbd_dev = container_of(ws_nbd, struct nbd_device,
> +			ws_shutdown);
> +
> +	sock_shutdown(nbd_dev);
> +}
> +
>  #if IS_ENABLED(CONFIG_DEBUG_FS)
> 
>  static int nbd_dbg_tasks_show(struct seq_file *s, void *unused)

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[PATCH v4 0/4] nbd: nbd fixes "Pranay Kr. Srivastava" <pranjas@gmail.com> - 2016-06-30 13:10 +0200
  [PATCH v4 1/5]nbd: cleanup nbd_set_socket "Pranay Kr. Srivastava" <pranjas@gmail.com> - 2016-06-30 13:10 +0200
    Re: [PATCH v4 1/5]nbd: cleanup nbd_set_socket Pranay Srivastava <pranjas@gmail.com> - 2016-07-07 17:00 +0200
      Re: [PATCH v4 1/5]nbd: cleanup nbd_set_socket Pranay Srivastava <pranjas@gmail.com> - 2016-07-09 09:40 +0200
  [PATCH v4 3/5]nbd: make nbd device wait for its users "Pranay Kr. Srivastava" <pranjas@gmail.com> - 2016-06-30 13:10 +0200
    Re: [PATCH v4 3/5]nbd: make nbd device wait for its users Markus Pargmann <mpa@pengutronix.de> - 2016-07-10 15:10 +0200
      Re: [PATCH v4 3/5]nbd: make nbd device wait for its users Pranay Srivastava <pranjas@gmail.com> - 2016-07-10 18:10 +0200
        Re: [PATCH v4 3/5]nbd: make nbd device wait for its users Markus Pargmann <mpa@pengutronix.de> - 2016-07-13 10:00 +0200
          Re: [PATCH v4 3/5]nbd: make nbd device wait for its users Pranay Srivastava <pranjas@gmail.com> - 2016-07-14 07:50 +0200
            [PATCH v5 3/4] make nbd device wait for its users Pranay Kr Srivastava <pranjas@gmail.com> - 2016-07-16 12:40 +0200
              Re: [PATCH v5 3/4] make nbd device wait for its users Pranay Srivastava <pranjas@gmail.com> - 2016-07-16 12:50 +0200
              Re: [PATCH v5 3/4] make nbd device wait for its users Markus Pargmann <mpa@pengutronix.de> - 2016-07-20 09:50 +0200
  [PATCH v4 4/5]nbd: use i_size_write to assign nbd device size "Pranay Kr. Srivastava" <pranjas@gmail.com> - 2016-06-30 13:10 +0200
  [PATCH v4 2/5]nbd: fix might_sleep warning on socket shutdown "Pranay Kr. Srivastava" <pranjas@gmail.com> - 2016-06-30 13:10 +0200
    Re: [PATCH v4 2/5]nbd: fix might_sleep warning on socket shutdown Pranay Srivastava <pranjas@gmail.com> - 2016-07-04 09:10 +0200
    Re: [PATCH v4 2/5]nbd: fix might_sleep warning on socket shutdown Markus Pargmann <mpa@pengutronix.de> - 2016-07-10 14:30 +0200
      Re: [PATCH v4 2/5]nbd: fix might_sleep warning on socket shutdown Markus Pargmann <mpa@pengutronix.de> - 2016-07-13 09:20 +0200
        Re: [PATCH v4 2/5]nbd: fix might_sleep warning on socket shutdown Pranay Srivastava <pranjas@gmail.com> - 2016-07-14 08:00 +0200
          [PATCH v5 2/4] nbd: fix might_sleep warning on socket shutdown. Pranay Kr Srivastava <pranjas@gmail.com> - 2016-07-16 11:30 +0200
            Re: [PATCH v5 2/4] nbd: fix might_sleep warning on socket shutdown. Pranay Srivastava <pranjas@gmail.com> - 2016-07-16 12:20 +0200
          (none) Pranay Kr Srivastava <pranjas@gmail.com> - 2016-07-16 11:30 +0200

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