[PATCH] scsi: storvsc: Prevent running tasklet for long

[Saurabh Sengar <ssengar@linux.microsoft.com>]

There can be scenarios where packets in ring buffer are continuously
getting queued from upper layer and dequeued from storvsc interrupt
handler, such scenarios can hold the foreach_vmbus_pkt loop (which is
executing as a tasklet) for a long duration. Theoretically its possible
that this loop executes forever. Add a condition to limit execution of
this tasklet for finite amount of time to avoid such hazardous scenarios.

Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
---
 drivers/scsi/storvsc_drv.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index fe000da..0c428cb 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -60,6 +60,9 @@
 #define VMSTOR_PROTO_VERSION_WIN8_1	VMSTOR_PROTO_VERSION(6, 0)
 #define VMSTOR_PROTO_VERSION_WIN10	VMSTOR_PROTO_VERSION(6, 2)
 
+/* channel callback timeout in ms */
+#define CALLBACK_TIMEOUT		5
+
 /*  Packet structure describing virtual storage requests. */
 enum vstor_packet_operation {
 	VSTOR_OPERATION_COMPLETE_IO		= 1,
@@ -1204,6 +1207,7 @@ static void storvsc_on_channel_callback(void *context)
 	struct hv_device *device;
 	struct storvsc_device *stor_device;
 	struct Scsi_Host *shost;
+	unsigned long expire = jiffies + msecs_to_jiffies(CALLBACK_TIMEOUT);
 
 	if (channel->primary_channel != NULL)
 		device = channel->primary_channel->device_obj;
@@ -1224,6 +1228,9 @@ static void storvsc_on_channel_callback(void *context)
 		u32 minlen = rqst_id ? sizeof(struct vstor_packet) :
 			sizeof(enum vstor_packet_operation);
 
+		if (time_after(jiffies, expire))
+			break;
+
 		if (pktlen < minlen) {
 			dev_err(&device->device,
 				"Invalid pkt: id=%llu, len=%u, minlen=%u\n",
-- 
1.8.3.1