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Date: Thu, 19 May 2016 08:22:13 +0200
From: Markus Pargmann <mpa@...gutronix.de>
To: "Pranay Kr. Srivastava" <pranjas@...il.com>
Cc: nbd-general@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
gregkh@...uxfoundation.org
Subject: Re: [PATCH v4 01/18] nbd: Fix might_sleep warning on xmit timeout
Hi,
On Wed, May 11, 2016 at 11:18:29AM +0300, Pranay Kr. Srivastava wrote:
> This patch fixes the warning generated when a timeout occurs
> on the request and socket is closed from a non-sleep context
> by
>
> 1. Moving the socket closing on a timeout to nbd_thread_send
What happens if a send blocks?
>
> 2. Make sock lock to be a mutex instead of a spin lock, since
> nbd_xmit_timeout doesn't need to hold it anymore.
I can't see why we need a mutex instead of a spinlock?
>
> Signed-off-by: Pranay Kr. Srivastava <pranjas@...il.com>
> ---
> drivers/block/nbd.c | 65 ++++++++++++++++++++++++++++++++---------------------
> 1 file changed, 39 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 31e73a7..c79bcd7 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -57,12 +57,12 @@ struct nbd_device {
> int blksize;
> loff_t bytesize;
> int xmit_timeout;
> - bool timedout;
> + atomic_t timedout;
> bool disconnect; /* a disconnect has been requested by user */
>
> struct timer_list timeout_timer;
> /* protects initialization and shutdown of the socket */
> - spinlock_t sock_lock;
> + struct mutex sock_lock;
> struct task_struct *task_recv;
> struct task_struct *task_send;
>
> @@ -172,10 +172,9 @@ 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);
> -
> + mutex_lock(&nbd->sock_lock);
> if (!nbd->sock) {
> - spin_unlock_irq(&nbd->sock_lock);
> + mutex_unlock(&nbd->sock_lock);
> return;
> }
>
> @@ -183,27 +182,19 @@ static void sock_shutdown(struct nbd_device *nbd)
> kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
> sockfd_put(nbd->sock);
> nbd->sock = NULL;
> - spin_unlock_irq(&nbd->sock_lock);
> -
> + mutex_unlock(&nbd->sock_lock);
> del_timer(&nbd->timeout_timer);
> }
>
> 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);
> + wake_up(&nbd->waiting_wq);
>
> dev_err(nbd_to_dev(nbd), "Connection timed out, shutting down connection\n");
> }
> @@ -579,7 +570,27 @@ static int nbd_thread_send(void *data)
> /* wait for something to do */
> wait_event_interruptible(nbd->waiting_wq,
> kthread_should_stop() ||
> - !list_empty(&nbd->waiting_queue));
> + !list_empty(&nbd->waiting_queue) ||
> + atomic_read(&nbd->timedout));
> +
> + if (atomic_read(&nbd->timedout)) {
> + mutex_lock(&nbd->sock_lock);
> + if (nbd->sock) {
> + struct request sreq;
> +
> + blk_rq_init(NULL, &sreq);
> + sreq.cmd_type = REQ_TYPE_DRV_PRIV;
> + mutex_lock(&nbd->tx_lock);
> + nbd->disconnect = true;
> + nbd_send_req(nbd, &sreq);
> + mutex_unlock(&nbd->tx_lock);
> + dev_err(disk_to_dev(nbd->disk),
> + "Device Timeout occured.Shutting down"
> + " socket.");
> + }
> + mutex_unlock(&nbd->sock_lock);
> + sock_shutdown(nbd);
Why are you trying to send something on a connection that timed out
(nbd_send_req())? And afterwards you execute a socket shutdown so in most
timeout cases this won't reach the server and we risk a blocking send on
a timedout connection.
Regards,
Markus
> + }
>
> /* extract request */
> if (list_empty(&nbd->waiting_queue))
> @@ -592,7 +603,11 @@ 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;
> @@ -647,7 +662,7 @@ static int nbd_set_socket(struct nbd_device *nbd, struct socket *sock)
> {
> int ret = 0;
>
> - spin_lock_irq(&nbd->sock_lock);
> + mutex_lock(&nbd->sock_lock);
>
> if (nbd->sock) {
> ret = -EBUSY;
> @@ -657,7 +672,7 @@ static int nbd_set_socket(struct nbd_device *nbd, struct socket *sock)
> nbd->sock = sock;
>
> out:
> - spin_unlock_irq(&nbd->sock_lock);
> + mutex_unlock(&nbd->sock_lock);
>
> return ret;
> }
> @@ -666,7 +681,7 @@ 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);
> @@ -803,17 +818,15 @@ 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);
> -
> - 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);
> @@ -1075,7 +1088,7 @@ static int __init nbd_init(void)
> nbd_dev[i].magic = NBD_MAGIC;
> INIT_LIST_HEAD(&nbd_dev[i].waiting_queue);
> spin_lock_init(&nbd_dev[i].queue_lock);
> - spin_lock_init(&nbd_dev[i].sock_lock);
> + mutex_init(&nbd_dev[i].sock_lock);
> INIT_LIST_HEAD(&nbd_dev[i].queue_head);
> mutex_init(&nbd_dev[i].tx_lock);
> init_timer(&nbd_dev[i].timeout_timer);
> --
> 2.6.2
>
>
--
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