RDMA/rxe: Limit the number of calls to each tasklet

Limit the maximum number of calls to each tasklet from rxe_do_task()
before yielding the cpu. When the limit is reached reschedule the tasklet
and exit the calling loop. This patch prevents one tasklet from consuming
100% of a cpu core and causing a deadlock or soft lockup.

Link: https://lore.kernel.org/r/20220630190425.2251-9-rpearsonhpe@gmail.com
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: Bob Pearson

drivers/infiniband/sw/rxe/rxe_param.h

@@ -105,6 +105,12 @@ enum rxe_device_param {
 	RXE_INFLIGHT_SKBS_PER_QP_HIGH	= 64,
 	RXE_INFLIGHT_SKBS_PER_QP_LOW	= 16,
 
+	/* Max number of interations of each tasklet
+	 * before yielding the cpu to let other
+	 * work make progress
+	 */
+	RXE_MAX_ITERATIONS		= 1024,
+
 	/* Delay before calling arbiter timer */
 	RXE_NSEC_ARB_TIMER_DELAY	= 200,
 

drivers/infiniband/sw/rxe/rxe_task.c

@@ -8,7 +8,7 @@
 #include <linux/interrupt.h>
 #include <linux/hardirq.h>
 
-#include "rxe_task.h"
+#include "rxe.h"
 
 int __rxe_do_task(struct rxe_task *task)
 
@@ -33,6 +33,7 @@ void rxe_do_task(struct tasklet_struct *t)
 	int cont;
 	int ret;
 	struct rxe_task *task = from_tasklet(task, t, tasklet);
+	unsigned int iterations = RXE_MAX_ITERATIONS;
 
 	spin_lock_bh(&task->state_lock);
 	switch (task->state) {
@@ -61,13 +62,20 @@ void rxe_do_task(struct tasklet_struct *t)
 		spin_lock_bh(&task->state_lock);
 		switch (task->state) {
 		case TASK_STATE_BUSY:
-			if (ret)
+			if (ret) {
 				task->state = TASK_STATE_START;
-			else
+			} else if (iterations--) {
 				cont = 1;
+			} else {
+				/* reschedule the tasklet and exit
+				 * the loop to give up the cpu
+				 */
+				tasklet_schedule(&task->tasklet);
+				task->state = TASK_STATE_START;
+			}
 			break;
 
-		/* soneone tried to run the task since the last time we called
+		/* someone tried to run the task since the last time we called
 		 * func, so we will call one more time regardless of the
 		 * return value
 		 */