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: 2ad4e6303a6d ("RDMA/bnxt_re: Implement doorbell pacing algorithm")
Link: https://patch.msgid.link/r/1728373302-19530-7-git-send-email-selvin.xavier@broadcom.com
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Reviewed-by: Chandramohan Akula <chandramohan.akula@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/infiniband/hw/bnxt_re/main.c b/drivers/infiniband/hw/bnxt_re/main.c
index 915b0d3a709a1734ea51cee7e0f6882a7f5cfc6e..b1dcb6bdac95035c986bbef1769a75eb083abab8 100644 (file)
--- a/drivers/infiniband/hw/bnxt_re/main.c
+++ b/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;
+               }
+
        }
 }