Re: [PATCH 1/4] fix might_sleep warning on socket shutdown.

Markus Pargmann
2016-05-30T12:06:12Z

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Hi,

On Tuesday 24 May 2016 14:26:25 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 | 62 +++++++++++++++++++++++++++++----------------------
> 1 file changed, 35 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 08afbc7..a5dab48 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;
> @@ -57,7 +58,7 @@ struct nbd_device {
> int blksize;
> loff_t bytesize;
> int xmit_timeout;
> - bool timedout;
> + atomic_t timedout;

Why are you using atomic here? It seems you are just counting the
occurences of timeouts with this but never actually use that number.

> bool disconnect; /* a disconnect has been requested by user */
>
> struct timer_list timeout_timer;
> @@ -69,6 +70,7 @@ struct nbd_device {
> #if IS_ENABLED(CONFIG_DEBUG_FS)
> struct dentry *dbg_dir;
> #endif
> + struct work_struct ws_nbd;

Can you rename this so that it is clear that this is a worker struct
specifically for the socket shutdown?

> };
>
> #if IS_ENABLED(CONFIG_DEBUG_FS)
> @@ -94,6 +96,7 @@ static int max_part;
> * Thanks go to Jens Axboe and Al Viro for their LKML emails explaining this!
> */
> static DEFINE_SPINLOCK(nbd_lock);
> +static void nbd_work_func(struct work_struct *);

Same here. nbd_work_func() doesn't give any hint about the real purpose
of the function.

>
> static inline struct device *nbd_to_dev(struct nbd_device *nbd)
> {
> @@ -172,39 +175,31 @@ 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);
> -
> + atomic_inc(&nbd->timedout);
> + schedule_work(&nbd->ws_nbd);
> + wake_up(&nbd->waiting_wq);
> dev_err(nbd_to_dev(nbd), "Connection timed out, shutting down connection\n");
> }
>
> @@ -592,7 +587,11 @@ static int nbd_thread_send(void *data)
> spin_unlock_irq(&nbd->queue_lock);
>
> /* handle request */
> - nbd_handle_req(nbd, req);
> + if (atomic_read(&nbd->timedout)) {
> + req->errors++;
> + nbd_end_request(nbd, req);
> + } else
> + nbd_handle_req(nbd, req);
> }
>
> nbd->task_send = NULL;
> @@ -666,12 +665,13 @@ out:
> static void nbd_reset(struct nbd_device *nbd)
> {
> nbd->disconnect = false;
> - nbd->timedout = false;
> + atomic_set(&nbd->timedout, 0);
> nbd->blksize = 1024;
> nbd->bytesize = 0;
> set_capacity(nbd->disk, 0);
> nbd->flags = 0;
> nbd->xmit_timeout = 0;
> + INIT_WORK(&nbd->ws_nbd, nbd_work_func);
> queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
> del_timer_sync(&nbd->timeout_timer);
> }
> @@ -804,16 +804,16 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
> nbd_dev_dbg_close(nbd);
> kthread_stop(thread);
>
> - mutex_lock(&nbd->tx_lock);
> -
> sock_shutdown(nbd);
> + mutex_lock(&nbd->tx_lock);
> nbd_clear_que(nbd);
> kill_bdev(bdev);
> nbd_bdev_reset(bdev);
>
> if (nbd->disconnect) /* user requested, ignore socket errors */
> error = 0;
> - if (nbd->timedout)
> +
> + if (atomic_read(&nbd->timedout))
> error = -ETIMEDOUT;
>
> nbd_reset(nbd);
> @@ -863,6 +863,14 @@ static const struct block_device_operations nbd_fops =
> .compat_ioctl = nbd_ioctl,
> };
>
> +static void nbd_work_func(struct work_struct *ws_nbd)
> +{
> + struct nbd_device *nbd_dev = container_of(ws_nbd, struct nbd_device,
> + ws_nbd);

Please align line breaks on the opening bracket.

Best Regards,

Markus

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