Re: [PATCH v2 1/5] nbd: fix might_sleep warning on socket shutdown.

[Pranay Srivastava <pranjas@gmail.com>]

Hi

On Tue, Jun 14, 2016 at 2:22 PM, Markus Pargmann <mpa@pengutronix.de> wrote:
> Hi,
>
> On Thursday 02 June 2016 13:24:57 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>
>
> This looks better. Some smaller things inline. Also this patch does not
> apply on my tree anymore. Can you please rebase it onto:
>         http://git.pengutronix.de/?p=mpa/linux-nbd.git;a=shortlog;h=refs/heads/master
>

Ok will do.

>> ---
>>  drivers/block/nbd.c | 65 ++++++++++++++++++++++++++++++++++-------------------
>>  1 file changed, 42 insertions(+), 23 deletions(-)
>>
>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
>> index 31e73a7..0339d40 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 +182,35 @@ 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);
>> +     /*
>> +      * Make sure sender thread sees nbd->timedout.
>> +      */
>> +     smp_wmb();
>
> I am not sure that we need this memory barrier here. But as it is just
> the timeout path it probably won't hurt.
>
>> +     wake_up(&nbd->waiting_wq);
>>       dev_err(nbd_to_dev(nbd), "Connection timed out, shutting down connection\n");
>>  }
>>
>> @@ -592,7 +598,11 @@ 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);
>>       }
>>
>>       nbd->task_send = NULL;
>> @@ -672,6 +682,7 @@ 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);
>>  }
>> @@ -804,15 +815,15 @@ 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;
>> +
>
> Random newline here.
Ok, will take care of this.

>
> Best Regards,
>
> Markus
>
>>               if (nbd->timedout)
>>                       error = -ETIMEDOUT;
>>
>> @@ -863,6 +874,14 @@ 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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