RDMA/bnxt_re: Avoid CPU lockups due fifo occupancy check loop

Driver waits indefinitely for the fifo occupancy to go below a threshold
as soon as the pacing interrupt is received. This can cause soft lockup on
one of the processors, if the rate of DB is very high.

Add a loop count for FPGA and exit the __wait_for_fifo_occupancy_below_th
if the loop is taking more time. Pacing will be continuing until the
occupancy is below the threshold. This is ensured by the checks in
bnxt_re_pacing_timer_exp and further scheduling the work for pacing based
on the fifo occupancy.

Fixes: 2ad4e63 ("RDMA/bnxt_re: Implement doorbell pacing algorithm")
Link: https://patch.msgid.link/r/[email protected]
Reviewed-by: Kalesh AP <[email protected]>
Reviewed-by: Chandramohan Akula <[email protected]>
Signed-off-by: Selvin Xavier <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: selvintxavier

drivers/infiniband/hw/bnxt_re/main.c

@@ -534,6 +534,7 @@ static bool is_dbr_fifo_full(struct bnxt_re_dev *rdev)
 static void __wait_for_fifo_occupancy_below_th(struct bnxt_re_dev *rdev)
 {
 	struct bnxt_qplib_db_pacing_data *pacing_data = rdev->qplib_res.pacing_data;
+	u32 retry_fifo_check = 1000;
 	u32 fifo_occup;
 
 	/* loop shouldn't run infintely as the occupancy usually goes
@@ -547,6 +548,14 @@ static void __wait_for_fifo_occupancy_below_th(struct bnxt_re_dev *rdev)
 
 		if (fifo_occup < pacing_data->pacing_th)
 			break;
+		if (!retry_fifo_check--) {
+			dev_info_once(rdev_to_dev(rdev),
+				      "%s: fifo_occup = 0x%xfifo_max_depth = 0x%x pacing_th = 0x%x\n",
+				      __func__, fifo_occup, pacing_data->fifo_max_depth,
+					pacing_data->pacing_th);
+			break;
+		}
+
 	}
 }