linux-kernel - Re: [PATCH v5 2/4] nbd: fix might_sleep warning on socket shutdown.

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Message-ID: <CA+aCy1Fw3+apypaUru8wFnsmb=a9PkSZ9OoMC18=BB2yW37QZQ@mail.gmail.com>
Date:	Sat, 16 Jul 2016 15:44:50 +0530
From:	Pranay Srivastava <pranjas@...il.com>
To:	Markus Pargmann <mpa@...gutronix.de>,
	nbd-general@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Cc:	"Pranay Kr. Srivastava" <pranjas@...il.com>
Subject: Re: [PATCH v5 2/4] nbd: fix might_sleep warning on socket shutdown.

Hi Markus,

On Sat, Jul 16, 2016 at 2:52 PM, Pranay Kr Srivastava <pranjas@...il.com> wrote:
> From: "Pranay Kr. Srivastava" <pranjas@...il.com>
>
> 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>
>
> Changelog:
> Pranay Kr. Srivastava<pranjas@...il.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.
>
> v5)
>    removed unnecessary code as per review of v4).
>
> Signed-off-by: Pranay Kr Srivastava <pranjas@...il.com>
> ---
>  drivers/block/nbd.c | 53 +++++++++++++++++++++++++++++++----------------------
>  1 file changed, 31 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 766c401..4919760 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 +70,10 @@ 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 +100,11 @@ static int max_part;
>   */
>  static DEFINE_SPINLOCK(nbd_lock);
>
> +/*
> + * Shutdown function for nbd_dev work struct.
> + */
> +static void nbd_ws_func_shutdown(struct work_struct *);
> +
>  static inline struct device *nbd_to_dev(struct nbd_device *nbd)
>  {
>         return disk_to_dev(nbd->disk);
> @@ -172,39 +182,30 @@ 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);
> -
> +       schedule_work(&nbd->ws_shutdown);
>         dev_err(nbd_to_dev(nbd), "Connection timed out, shutting down connection\n");
>  }
>
> @@ -663,6 +664,7 @@ 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);
>  }
> @@ -798,10 +800,9 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>                 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 +858,14 @@ 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)
> --
> 2.6.2
>

Made the changes you suggested. Let me know if these look alright so I
can resend
the whole series.


-- 
        ---P.K.S