Re: [PATCH V2] block: add blk_io_schedule() for avoiding task hung in sync dio

[Satya Tangirala <satyat@google.com>]

On Sun, May 03, 2020 at 09:54:22AM +0800, Ming Lei wrote:
> Sync dio could be big, or may take long time in discard or in case of
> IO failure.
> 
> We have prevented task hung in submit_bio_wait() and blk_execute_rq(),
> so apply the same trick for prevent task hung from happening in sync dio.
> 
> Add helper of blk_io_schedule() and use io_schedule_timeout() to prevent
> task hung warning.
> 
> Cc: Salman Qazi <sqazi@google.com>
> Cc: Jesse Barnes <jsbarnes@google.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Bart Van Assche <bvanassche@acm.org>
> Cc: Hannes Reinecke <hare@suse.de>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> V2:
> 	- drop helper of blk_default_io_timeout()
> 
> 
>  fs/block_dev.c         |  4 ++--
>  fs/direct-io.c         |  2 +-
>  fs/iomap/direct-io.c   |  2 +-
>  include/linux/blkdev.h | 12 ++++++++++++
>  4 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 5eb30a474f6d..3b396f8c967c 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -256,7 +256,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
>  			break;
>  		if (!(iocb->ki_flags & IOCB_HIPRI) ||
>  		    !blk_poll(bdev_get_queue(bdev), qc, true))
> -			io_schedule();
> +			blk_io_schedule();
>  	}
>  	__set_current_state(TASK_RUNNING);
>  
> @@ -450,7 +450,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>  
>  		if (!(iocb->ki_flags & IOCB_HIPRI) ||
>  		    !blk_poll(bdev_get_queue(bdev), qc, true))
> -			io_schedule();
> +			blk_io_schedule();
>  	}
>  	__set_current_state(TASK_RUNNING);
>  
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 00b4d15bb811..6d5370eac2a8 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -500,7 +500,7 @@ static struct bio *dio_await_one(struct dio *dio)
>  		spin_unlock_irqrestore(&dio->bio_lock, flags);
>  		if (!(dio->iocb->ki_flags & IOCB_HIPRI) ||
>  		    !blk_poll(dio->bio_disk->queue, dio->bio_cookie, true))
> -			io_schedule();
> +			blk_io_schedule();
>  		/* wake up sets us TASK_RUNNING */
>  		spin_lock_irqsave(&dio->bio_lock, flags);
>  		dio->waiter = NULL;
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 20dde5aadcdd..fd3bd06fabb6 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -561,7 +561,7 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  			    !dio->submit.last_queue ||
>  			    !blk_poll(dio->submit.last_queue,
>  					 dio->submit.cookie, true))
> -				io_schedule();
> +				blk_io_schedule();
>  		}
>  		__set_current_state(TASK_RUNNING);
>  	}
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index f00bd4042295..222eb5f32279 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -27,6 +27,7 @@
>  #include <linux/percpu-refcount.h>
>  #include <linux/scatterlist.h>
>  #include <linux/blkzoned.h>
> +#include <linux/sched/sysctl.h>
>  
>  struct module;
>  struct scsi_ioctl_command;
> @@ -1827,4 +1828,15 @@ static inline void blk_wake_io_task(struct task_struct *waiter)
>  		wake_up_process(waiter);
>  }
>  
> +static inline void blk_io_schedule(void)
> +{
> +	/* Prevent hang_check timer from firing at us during very long I/O */
> +	unsigned long timeout = sysctl_hung_task_timeout_secs * HZ / 2;
> +
> +	if (timeout)
> +		io_schedule_timeout(timeout);
> +	else
> +		io_schedule();
> +}
> +
>  #endif
This won't compile without CONFIG_BLOCK, since this patch includes
linux/sched/sysctl.h only inside the #ifdef CONFIG_BLOCK, while blk_io_schedule
is declared outside the #ifdef CONFIG_BLOCK, but references
sysctl_hung_task_timeout_secs defined in linux/sched/sysctl.h. Afaict, the
function isn't needed without CONFIG_BLOCK, so maybe we should move the
function into the #ifdef CONFIG_BLOCK too?

> -- 
> 2.25.2
>