[PATCH] blkfront: Move blkif_interrupt into a tasklet.

[Daniel Stodden <daniel.stodden@citrix.com>]

Response processing doesn't really belong into hard irq context.

Another potential problem this avoids is that switching interrupt cpu
affinity in Xen domains can presently lead to event loss, if
RING_FINAL_CHECK is run from hard irq context.

Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
Cc: Tom Kopec <tek@acm.org>
---
 drivers/block/xen-blkfront.c |   16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 6c00538..75576d3 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -86,6 +86,7 @@ struct blkfront_info
 	struct blkif_front_ring ring;
 	struct scatterlist sg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
 	unsigned int evtchn, irq;
+	struct tasklet_struct tasklet;
 	struct request_queue *rq;
 	struct work_struct work;
 	struct gnttab_free_callback callback;
@@ -676,13 +677,14 @@ static void blkif_completion(struct blk_shadow *s)
 		gnttab_end_foreign_access(s->req.seg[i].gref, 0, 0UL);
 }
 
-static irqreturn_t blkif_interrupt(int irq, void *dev_id)
+static void
+blkif_do_interrupt(unsigned long data)
 {
+	struct blkfront_info *info = (struct blkfront_info *)data;
 	struct request *req;
 	struct blkif_response *bret;
 	RING_IDX i, rp;
 	unsigned long flags;
-	struct blkfront_info *info = (struct blkfront_info *)dev_id;
 	int error;
 
 	spin_lock_irqsave(&info->io_lock, flags);
@@ -743,6 +745,15 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 
 out:
 	spin_unlock_irqrestore(&info->io_lock, flags);
+}
+
+
+static irqreturn_t
+blkif_interrupt(int irq, void *dev_id)
+{
+	struct blkfront_info *info = (struct blkfront_info *)dev_id;
+
+	tasklet_schedule(&info->tasklet);
 
 	return IRQ_HANDLED;
 }
@@ -893,6 +904,7 @@ static int blkfront_probe(struct xenbus_device *dev,
 	info->connected = BLKIF_STATE_DISCONNECTED;
 	INIT_WORK(&info->work, blkif_restart_queue);
 	spin_lock_init(&info->io_lock);
+	tasklet_init(&info->tasklet, blkif_do_interrupt, (unsigned long)info);
 
 	for (i = 0; i < BLK_RING_SIZE; i++)
 		info->shadow[i].req.id = i+1;
-- 
1.7.0.4