Patch "RDMA/bnxt_re: Avoid CPU lockups due fifo occupancy check loop" has been added to the 6.11-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 6.11-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     rdma-bnxt_re-avoid-cpu-lockups-due-fifo-occupancy-ch.patch
and it can be found in the queue-6.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 43ffdd84a83dcbe8f037153a2156d4ee8001f8c0
Author: Selvin Xavier <selvin.xavier@xxxxxxxxxxxx>
Date:   Tue Oct 8 00:41:38 2024 -0700

    RDMA/bnxt_re: Avoid CPU lockups due fifo occupancy check loop
    
    [ Upstream commit 8be3e5b0c96beeefe9d5486b96575d104d3e7d17 ]
    
    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@xxxxxxxxxxxx
    Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@xxxxxxxxxxxx>
    Reviewed-by: Chandramohan Akula <chandramohan.akula@xxxxxxxxxxxx>
    Signed-off-by: Selvin Xavier <selvin.xavier@xxxxxxxxxxxx>
    Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/infiniband/hw/bnxt_re/main.c b/drivers/infiniband/hw/bnxt_re/main.c
index e06adb2dfe6f9..c905a51aabfba 100644
--- a/drivers/infiniband/hw/bnxt_re/main.c
+++ b/drivers/infiniband/hw/bnxt_re/main.c
@@ -518,6 +518,7 @@ 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
@@ -531,6 +532,14 @@ 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;
+		}
+
 	}
 }