sunvdc: Do not spin in an infinite loop when vio_ldc_send() returns EAGAIN

BugLink: https://bugs.launchpad.net/bugs/1818813

[ Upstream commit a11f6ca9 ]

__vdc_tx_trigger should only loop on EAGAIN a finite
number of times.

See commit adddc32d ("sunvnet: Do not spin in an
infinite loop when vio_ldc_send() returns EAGAIN") for detail.
Signed-off-by: Young Xiao <YangX92@hotmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/block/sunvdc.c

@@ -40,6 +40,8 @@ MODULE_VERSION(DRV_MODULE_VERSION);
 #define WAITING_FOR_GEN_CMD	0x04
 #define WAITING_FOR_ANY		-1
 
+#define	VDC_MAX_RETRIES	10
+
 static struct workqueue_struct *sunvdc_wq;
 
 struct vdc_req_entry {
@@ -419,6 +421,7 @@ static int __vdc_tx_trigger(struct vdc_port *port)
 		.end_idx		= dr->prod,
 	};
 	int err, delay;
+	int retries = 0;
 
 	hdr.seq = dr->snd_nxt;
 	delay = 1;
@@ -431,6 +434,8 @@ static int __vdc_tx_trigger(struct vdc_port *port)
 		udelay(delay);
 		if ((delay <<= 1) > 128)
 			delay = 128;
+		if (retries++ > VDC_MAX_RETRIES)
+			break;
 	} while (err == -EAGAIN);
 
 	if (err == -ENOTCONN)