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Message-ID: <CA+aCy1GPTibWw9u0xqJCrjuhjuibighsKi+C0z5p=0PY0N9fww@mail.gmail.com>
Date: Fri, 20 May 2016 02:05:36 +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 v4 01/18] nbd: Fix might_sleep warning on xmit timeout
On Thu, May 19, 2016 at 11:52 AM, Markus Pargmann <mpa@...gutronix.de> wrote:
> 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?
socket closing needs to be moved to a non-atomic context and,
sender thread seemed to be a good place to do this. If you mean
send blocks just before calling sock_shutdown[?] in nbd_thread_send
then yes I think that should be removed. I need to re-check how nbd-server
behaves in that case.
>
>>
>> 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?
you are right, with your earlier patch we don't need it to be a mutex.
>
>>
>> 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.
Ok. I get it. But shouldn't the server side also close it's socket as
well? I don't
think the timeout value is propagated to server or like server can
"ping" to check
if client is there right?
I agree on nbd_send_req in timedout, it shouldn't be there, just a
sock_shutdown should
do. Can you confirm if I'm right about nbd-server side as well like it
won't timeout and close
that socket or did I miss any option while starting it?
>
> 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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