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Asias He

2012-May-21 09:08 UTC

[RFC PATCH 1/5] block: Introduce q->abort_queue_fn()

When user hot-unplug a disk which is busy serving I/O, __blk_run_queue
might be unable to drain all the requests. As a result, the
blk_drain_queue() would loop forever and blk_cleanup_queue would not
return. So hot-unplug will fail.

This patch adds a callback in blk_drain_queue() for low lever driver to
abort requests.

Currently, this is useful for virtio-blk to do cleanup in hot-unplug.

Cc: Jens Axboe <axboe at kernel.dk>
Cc: Tejun Heo <tj at kernel.org>
Cc: linux-fsdevel at vger.kernel.org
Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: virtualization at lists.linux-foundation.org
Cc: kvm at vger.kernel.org
Signed-off-by: Asias He <asias at redhat.com>
---
 block/blk-core.c       |    3 +++
 block/blk-settings.c   |   12 ++++++++++++
 include/linux/blkdev.h |    3 +++
 3 files changed, 18 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 1f61b74..ca42fd7 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -369,6 +369,9 @@ void blk_drain_queue(struct request_queue *q, bool
drain_all)
 		if (drain_all)
 			blk_throtl_drain(q);
 
+		if (q->abort_queue_fn)
+			q->abort_queue_fn(q);
+
 		/*
 		 * This function might be called on a queue which failed
 		 * driver init after queue creation.  Some drivers
diff --git a/block/blk-settings.c b/block/blk-settings.c
index d3234fc..83ccb48 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -100,6 +100,18 @@ void blk_queue_lld_busy(struct request_queue *q,
lld_busy_fn *fn)
 EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
 
 /**
+ * blk_queue_abort_queue - set driver specific abort function
+ * @q:		queue
+ * @mbfn:	abort_queue_fn
+ */
+void blk_queue_abort_queue(struct request_queue *q, abort_queue_fn *afn)
+{
+	q->abort_queue_fn = afn;
+}
+EXPORT_SYMBOL(blk_queue_abort_queue);
+
+
+/**
  * blk_set_default_limits - reset limits to default values
  * @lim:  the queue_limits structure to reset
  *
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2aa2466..e2d58bd 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -200,6 +200,7 @@ struct request_pm_state
 
 typedef void (request_fn_proc) (struct request_queue *q);
 typedef void (make_request_fn) (struct request_queue *q, struct bio *bio);
+typedef void (abort_queue_fn) (struct request_queue *q);
 typedef int (prep_rq_fn) (struct request_queue *, struct request *);
 typedef void (unprep_rq_fn) (struct request_queue *, struct request *);
 
@@ -282,6 +283,7 @@ struct request_queue {
 
 	request_fn_proc		*request_fn;
 	make_request_fn		*make_request_fn;
+	abort_queue_fn		*abort_queue_fn;
 	prep_rq_fn		*prep_rq_fn;
 	unprep_rq_fn		*unprep_rq_fn;
 	merge_bvec_fn		*merge_bvec_fn;
@@ -821,6 +823,7 @@ extern struct request_queue *blk_init_allocated_queue(struct
request_queue *,
 						      request_fn_proc *, spinlock_t *);
 extern void blk_cleanup_queue(struct request_queue *);
 extern void blk_queue_make_request(struct request_queue *, make_request_fn *);
+extern void blk_queue_abort_queue(struct request_queue *, abort_queue_fn *);
 extern void blk_queue_bounce_limit(struct request_queue *, u64);
 extern void blk_limits_max_hw_sectors(struct queue_limits *, unsigned int);
 extern void blk_queue_max_hw_sectors(struct request_queue *, unsigned int);
-- 
1.7.10.1

Asias He

2012-May-21 09:08 UTC

head link

[RFC PATCH 3/5] virtio-blk: Call del_gendisk() before disable guest kick

del_gendisk() might not return due to failing to remove the
/sys/block/vda/serial sysfs entry when another thread (udev) is
trying to read it.

virtblk_remove()
  vdev->config->reset() : guest will not kick us through interrupt
    del_gendisk()
      device_del()
        kobject_del(): got stuck, sysfs entry ref count non zero

sysfs_open_file(): user space process read /sys/block/vda/serial
   sysfs_get_active() : got sysfs entry ref count
      dev_attr_show()
        virtblk_serial_show()
           blk_execute_rq() : got stuck, interrupt is disabled
                              request cannot be finished

This patch fixes it by calling del_gendisk() before we disable guest's
interrupt so that the request sent in virtblk_serial_show() will be
finished and del_gendisk() will success.

This fixes another race in hot-unplug process.

It is save to call del_gendisk(vblk->disk) before
flush_work(&vblk->config_work) which might access vblk->disk, because
vblk->disk is not freed until put_disk(vblk->disk).

Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: virtualization at lists.linux-foundation.org
Cc: kvm at vger.kernel.org
Signed-off-by: Asias He <asias at redhat.com>
---
 drivers/block/virtio_blk.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 693187d..7d5f5b0 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -584,12 +584,13 @@ static void __devexit virtblk_remove(struct virtio_device
*vdev)
 	vblk->config_enable = false;
 	mutex_unlock(&vblk->config_lock);
 
+	del_gendisk(vblk->disk);
+
 	/* Stop all the virtqueues. */
 	vdev->config->reset(vdev);
 
 	flush_work(&vblk->config_work);
 
-	del_gendisk(vblk->disk);
 
 	/* Abort requests dispatched to driver. */
 	spin_lock_irqsave(&vblk->lock, flags);
-- 
1.7.10.1

Asias He

2012-May-21 09:08 UTC

head link

[RFC PATCH 4/5] virtio-blk: Use q->abort_queue_fn() to abort requests

virtblk_abort_queue() will be called by the block layer when cleans up
the queue. blk_cleanup_queue -> blk_drain_queue() ->
q->abort_queue_fn(q)

virtblk_abort_queue()
1) Abort requests in block which is not dispatched to driver
2) Abort requests already dispatched to driver
3) Wake up processes which is sleeping on get_request_wait()

This makes hot-unplug a disk which is busy serving I/O success.

Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: virtualization at lists.linux-foundation.org
Cc: kvm at vger.kernel.org
Cc: Jens Axboe <axboe at kernel.dk>
Cc: Tejun Heo <tj at kernel.org>
Cc: linux-fsdevel at vger.kernel.org
Signed-off-by: Asias He <asias at redhat.com>
---
 drivers/block/virtio_blk.c |   38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 7d5f5b0..ba35509 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -182,6 +182,31 @@ static bool do_req(struct request_queue *q, struct
virtio_blk *vblk,
 	return true;
 }
 
+void virtblk_abort_queue(struct request_queue *q)
+{
+	struct virtio_blk *vblk = q->queuedata;
+	struct virtblk_req *vbr;
+	int i;
+
+	/* Abort requests in block layer. */
+	elv_abort_queue(q);
+
+	/* Abort requests dispatched to driver. */
+	while ((vbr = virtqueue_detach_unused_buf(vblk->vq))) {
+		vbr->req->cmd_flags |= REQ_QUIET;
+		__blk_end_request_all(vbr->req, -EIO);
+		mempool_free(vbr, vblk->pool);
+	}
+
+	/* Wake up threads sleeping on get_request_wait() */
+	for (i = 0; i < ARRAY_SIZE(q->rq.wait); i++) {
+		if (waitqueue_active(&q->rq.wait[i]))
+			wake_up_all(&q->rq.wait[i]);
+	}
+
+	return;
+}
+
 static void do_virtblk_request(struct request_queue *q)
 {
 	struct virtio_blk *vblk = q->queuedata;
@@ -462,6 +487,8 @@ static int __devinit virtblk_probe(struct virtio_device
*vdev)
 		goto out_put_disk;
 	}
 
+	blk_queue_abort_queue(q, virtblk_abort_queue);
+
 	q->queuedata = vblk;
 
 	virtblk_name_format("vd", index, vblk->disk->disk_name,
DISK_NAME_LEN);
@@ -576,8 +603,6 @@ static void __devexit virtblk_remove(struct virtio_device
*vdev)
 {
 	struct virtio_blk *vblk = vdev->priv;
 	int index = vblk->index;
-	struct virtblk_req *vbr;
-	unsigned long flags;
 
 	/* Prevent config work handler from accessing the device. */
 	mutex_lock(&vblk->config_lock);
@@ -591,15 +616,6 @@ static void __devexit virtblk_remove(struct virtio_device
*vdev)
 
 	flush_work(&vblk->config_work);
 
-
-	/* Abort requests dispatched to driver. */
-	spin_lock_irqsave(&vblk->lock, flags);
-	while ((vbr = virtqueue_detach_unused_buf(vblk->vq))) {
-		__blk_end_request_all(vbr->req, -EIO);
-		mempool_free(vbr, vblk->pool);
-	}
-	spin_unlock_irqrestore(&vblk->lock, flags);
-
 	blk_cleanup_queue(vblk->disk->queue);
 	put_disk(vblk->disk);
 	mempool_destroy(vblk->pool);
-- 
1.7.10.1

Asias He

2012-May-21 09:08 UTC

head link

[RFC PATCH 5/5] virtio-blk: Use block layer provided spinlock

Block layer will allocate a spinlock for the queue if the driver does
not provide one in blk_init_queue().

The reason to use the internal spinlock is that blk_cleanup_queue() will
switch to use the internal spinlock in the cleanup code path.
        if (q->queue_lock != &q->__queue_lock)
                q->queue_lock = &q->__queue_lock;

However, processes which are in D state might have taken the driver
provided spinlock, when the processes wake up , they would release the
block provided spinlock.

====================================[ BUG: bad unlock balance detected! ]
3.4.0-rc7+ #238 Not tainted
-------------------------------------
fio/3587 is trying to release lock (&(&q->__queue_lock)->rlock)
at:
[<ffffffff813274d2>] blk_queue_bio+0x2a2/0x380
but there are no more locks to release!

other info that might help us debug this:
1 lock held by fio/3587:
 #0:  (&(&vblk->lock)->rlock){......}, at:
[<ffffffff8132661a>] get_request_wait+0x19a/0x250

Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: virtualization at lists.linux-foundation.org
Cc: kvm at vger.kernel.org
Signed-off-by: Asias He <asias at redhat.com>
---
 drivers/block/virtio_blk.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index ba35509..0c2f0e8 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -21,8 +21,6 @@ struct workqueue_struct *virtblk_wq;
 
 struct virtio_blk
 {
-	spinlock_t lock;
-
 	struct virtio_device *vdev;
 	struct virtqueue *vq;
 
@@ -65,7 +63,7 @@ static void blk_done(struct virtqueue *vq)
 	unsigned int len;
 	unsigned long flags;
 
-	spin_lock_irqsave(&vblk->lock, flags);
+	spin_lock_irqsave(vblk->disk->queue->queue_lock, flags);
 	while ((vbr = virtqueue_get_buf(vblk->vq, &len)) != NULL) {
 		int error;
 
@@ -99,7 +97,7 @@ static void blk_done(struct virtqueue *vq)
 	}
 	/* In case queue is stopped waiting for more buffers. */
 	blk_start_queue(vblk->disk->queue);
-	spin_unlock_irqrestore(&vblk->lock, flags);
+	spin_unlock_irqrestore(vblk->disk->queue->queue_lock, flags);
 }
 
 static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
@@ -456,7 +454,6 @@ static int __devinit virtblk_probe(struct virtio_device
*vdev)
 		goto out_free_index;
 	}
 
-	spin_lock_init(&vblk->lock);
 	vblk->vdev = vdev;
 	vblk->sg_elems = sg_elems;
 	sg_init_table(vblk->sg, vblk->sg_elems);
@@ -481,7 +478,7 @@ static int __devinit virtblk_probe(struct virtio_device
*vdev)
 		goto out_mempool;
 	}
 
-	q = vblk->disk->queue = blk_init_queue(do_virtblk_request,
&vblk->lock);
+	q = vblk->disk->queue = blk_init_queue(do_virtblk_request, NULL);
 	if (!q) {
 		err = -ENOMEM;
 		goto out_put_disk;
-- 
1.7.10.1

Tejun Heo

2012-May-21 15:42 UTC

head link

[RFC PATCH 1/5] block: Introduce q->abort_queue_fn()

On Mon, May 21, 2012 at 05:08:29PM +0800, Asias He
wrote:> When user hot-unplug a disk which is busy serving I/O, __blk_run_queue
> might be unable to drain all the requests. As a result, the
> blk_drain_queue() would loop forever and blk_cleanup_queue would not
> return. So hot-unplug will fail.
> 
> This patch adds a callback in blk_drain_queue() for low lever driver to
> abort requests.
> 
> Currently, this is useful for virtio-blk to do cleanup in hot-unplug.
Why is this necessary?  virtio-blk should know that the device is gone
and fail in-flight / new commands.  That's what other drivers do.
What makes virtio-blk different?

Thanks.

-- 
tejun

Michael S. Tsirkin

2012-May-21 20:59 UTC

head link

[RFC PATCH 5/5] virtio-blk: Use block layer provided spinlock

On Mon, May 21, 2012 at 05:08:33PM +0800, Asias He
wrote:> Block layer will allocate a spinlock for the queue if the driver does
> not provide one in blk_init_queue().
> 
> The reason to use the internal spinlock is that blk_cleanup_queue() will
> switch to use the internal spinlock in the cleanup code path.
>         if (q->queue_lock != &q->__queue_lock)
>                 q->queue_lock = &q->__queue_lock;
> 
> However, processes which are in D state might have taken the driver
> provided spinlock, when the processes wake up , they would release the
> block provided spinlock.
Are you saying any driver with its own spinlock is
broken if hotunplugged under stress?
> ====================================> [ BUG: bad unlock balance
detected! ]
> 3.4.0-rc7+ #238 Not tainted
> -------------------------------------
> fio/3587 is trying to release lock
(&(&q->__queue_lock)->rlock) at:
> [<ffffffff813274d2>] blk_queue_bio+0x2a2/0x380
> but there are no more locks to release!
> 
> other info that might help us debug this:
> 1 lock held by fio/3587:
>  #0:  (&(&vblk->lock)->rlock){......}, at:
> [<ffffffff8132661a>] get_request_wait+0x19a/0x250
> 
> Cc: Rusty Russell <rusty at rustcorp.com.au>
> Cc: "Michael S. Tsirkin" <mst at redhat.com>
> Cc: virtualization at lists.linux-foundation.org
> Cc: kvm at vger.kernel.org
> Signed-off-by: Asias He <asias at redhat.com>
> ---
>  drivers/block/virtio_blk.c |    9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index ba35509..0c2f0e8 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -21,8 +21,6 @@ struct workqueue_struct *virtblk_wq;
>  
>  struct virtio_blk
>  {
> -	spinlock_t lock;
> -
>  	struct virtio_device *vdev;
>  	struct virtqueue *vq;
>  
> @@ -65,7 +63,7 @@ static void blk_done(struct virtqueue *vq)
>  	unsigned int len;
>  	unsigned long flags;
>  
> -	spin_lock_irqsave(&vblk->lock, flags);
> +	spin_lock_irqsave(vblk->disk->queue->queue_lock, flags);
>  	while ((vbr = virtqueue_get_buf(vblk->vq, &len)) != NULL) {
>  		int error;
>  
> @@ -99,7 +97,7 @@ static void blk_done(struct virtqueue *vq)
>  	}
>  	/* In case queue is stopped waiting for more buffers. */
>  	blk_start_queue(vblk->disk->queue);
> -	spin_unlock_irqrestore(&vblk->lock, flags);
> +	spin_unlock_irqrestore(vblk->disk->queue->queue_lock, flags);
>  }
>  
>  static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
> @@ -456,7 +454,6 @@ static int __devinit virtblk_probe(struct virtio_device
*vdev)
>  		goto out_free_index;
>  	}
>  
> -	spin_lock_init(&vblk->lock);
>  	vblk->vdev = vdev;
>  	vblk->sg_elems = sg_elems;
>  	sg_init_table(vblk->sg, vblk->sg_elems);
> @@ -481,7 +478,7 @@ static int __devinit virtblk_probe(struct virtio_device
*vdev)
>  		goto out_mempool;
>  	}
>  
> -	q = vblk->disk->queue = blk_init_queue(do_virtblk_request,
&vblk->lock);
> +	q = vblk->disk->queue = blk_init_queue(do_virtblk_request, NULL);
>  	if (!q) {
>  		err = -ENOMEM;
>  		goto out_put_disk;
> -- 
> 1.7.10.1

Asias He

2012-May-22 08:22 UTC

head link

[RFC PATCH 5/5] virtio-blk: Use block layer provided spinlock

On 05/22/2012 04:59 AM, Michael S. Tsirkin wrote:> On Mon, May 21, 2012 at 05:08:33PM +0800, Asias He wrote:
>> Block layer will allocate a spinlock for the queue if the driver does
>> not provide one in blk_init_queue().
>>
>> The reason to use the internal spinlock is that blk_cleanup_queue()
will
>> switch to use the internal spinlock in the cleanup code path.
>>          if (q->queue_lock !=&q->__queue_lock)
>>                  q->queue_lock =&q->__queue_lock;
>>
>> However, processes which are in D state might have taken the driver
>> provided spinlock, when the processes wake up , they would release the
>> block provided spinlock.
>
> Are you saying any driver with its own spinlock is
> broken if hotunplugged under stress?
Hi, Michael

I can not say that. It is very hard to find real hardware device to try 
this.  I tried on qemu with LSI Logic / Symbios Logic 53c895a scsi disk 
with hot-unplug. It is completely broken. And IDE does not support 
hotplug at all.

Do you see any downside of using the block provided spinlock?
>
>> ====================================>> [ BUG: bad unlock balance
detected! ]
>> 3.4.0-rc7+ #238 Not tainted
>> -------------------------------------
>> fio/3587 is trying to release lock
(&(&q->__queue_lock)->rlock) at:
>> [<ffffffff813274d2>] blk_queue_bio+0x2a2/0x380
>> but there are no more locks to release!
>>
>> other info that might help us debug this:
>> 1 lock held by fio/3587:
>>   #0:  (&(&vblk->lock)->rlock){......}, at:
>> [<ffffffff8132661a>] get_request_wait+0x19a/0x250
>>
>> Cc: Rusty Russell<rusty at rustcorp.com.au>
>> Cc: "Michael S. Tsirkin"<mst at redhat.com>
>> Cc: virtualization at lists.linux-foundation.org
>> Cc: kvm at vger.kernel.org
>> Signed-off-by: Asias He<asias at redhat.com>
>> ---
>>   drivers/block/virtio_blk.c |    9 +++------
>>   1 file changed, 3 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>> index ba35509..0c2f0e8 100644
>> --- a/drivers/block/virtio_blk.c
>> +++ b/drivers/block/virtio_blk.c
>> @@ -21,8 +21,6 @@ struct workqueue_struct *virtblk_wq;
>>
>>   struct virtio_blk
>>   {
>> -	spinlock_t lock;
>> -
>>   	struct virtio_device *vdev;
>>   	struct virtqueue *vq;
>>
>> @@ -65,7 +63,7 @@ static void blk_done(struct virtqueue *vq)
>>   	unsigned int len;
>>   	unsigned long flags;
>>
>> -	spin_lock_irqsave(&vblk->lock, flags);
>> +	spin_lock_irqsave(vblk->disk->queue->queue_lock, flags);
>>   	while ((vbr = virtqueue_get_buf(vblk->vq,&len)) != NULL) {
>>   		int error;
>>
>> @@ -99,7 +97,7 @@ static void blk_done(struct virtqueue *vq)
>>   	}
>>   	/* In case queue is stopped waiting for more buffers. */
>>   	blk_start_queue(vblk->disk->queue);
>> -	spin_unlock_irqrestore(&vblk->lock, flags);
>> +	spin_unlock_irqrestore(vblk->disk->queue->queue_lock,
flags);
>>   }
>>
>>   static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
>> @@ -456,7 +454,6 @@ static int __devinit virtblk_probe(struct
virtio_device *vdev)
>>   		goto out_free_index;
>>   	}
>>
>> -	spin_lock_init(&vblk->lock);
>>   	vblk->vdev = vdev;
>>   	vblk->sg_elems = sg_elems;
>>   	sg_init_table(vblk->sg, vblk->sg_elems);
>> @@ -481,7 +478,7 @@ static int __devinit virtblk_probe(struct
virtio_device *vdev)
>>   		goto out_mempool;
>>   	}
>>
>> -	q = vblk->disk->queue =
blk_init_queue(do_virtblk_request,&vblk->lock);
>> +	q = vblk->disk->queue = blk_init_queue(do_virtblk_request,
NULL);
>>   	if (!q) {
>>   		err = -ENOMEM;
>>   		goto out_put_disk;
>> --
>> 1.7.10.1

-- 
Asias

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