FAILED: patch "[PATCH] RDMA/rxe: Fix soft lockup problem due to using tasklets in" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 8ac0e6641c7ca14833a2a8c6f13d8e0a435e535c Mon Sep 17 00:00:00 2001
From: Zhu Yanjun <[email protected]>
Date: Wed, 12 Feb 2020 09:26:33 +0200
Subject: [PATCH] RDMA/rxe: Fix soft lockup problem due to using tasklets in
softirq

When run stress tests with RXE, the following Call Traces often occur

  watchdog: BUG: soft lockup - CPU#2 stuck for 22s! [swapper/2:0]
  ...
  Call Trace:
  <IRQ>
  create_object+0x3f/0x3b0
  kmem_cache_alloc_node_trace+0x129/0x2d0
  __kmalloc_reserve.isra.52+0x2e/0x80
  __alloc_skb+0x83/0x270
  rxe_init_packet+0x99/0x150 [rdma_rxe]
  rxe_requester+0x34e/0x11a0 [rdma_rxe]
  rxe_do_task+0x85/0xf0 [rdma_rxe]
  tasklet_action_common.isra.21+0xeb/0x100
  __do_softirq+0xd0/0x298
  irq_exit+0xc5/0xd0
  smp_apic_timer_interrupt+0x68/0x120
  apic_timer_interrupt+0xf/0x20
  </IRQ>
  ...

The root cause is that tasklet is actually a softirq. In a tasklet handler, another softirq handler is triggered. Usually these softirq handlers run on the same cpu core. So this will cause "soft lockup Bug".

index 116cafc9afcf..4bc88708b355 100644
@@ -329,7 +329,7 @@ static inline enum comp_state check_ack(struct rxe_qp *qp,
 					qp->comp.psn = pkt->psn;
 					if (qp->req.wait_psn) {
 						qp->req.wait_psn = 0;
-						rxe_run_task(&qp->req.task, 1);
+						rxe_run_task(&qp->req.task, 0);
 					}
 				}
 				return COMPST_ERROR_RETRY;

@@ -463,7 +463,7 @@ static void do_complete(struct rxe_qp *qp, struct rxe_send_wqe *wqe)
 	 */
 	if (qp->req.wait_fence) {
 		qp->req.wait_fence = 0;
-		rxe_run_task(&qp->req.task, 1);
+		rxe_run_task(&qp->req.task, 0);
 	}
 }
 

@@ -479,7 +479,7 @@ static inline enum comp_state complete_ack(struct rxe_qp *qp,
 		if (qp->req.need_rd_atomic) {
 			qp->comp.timeout_retry = 0;
 			qp->req.need_rd_atomic = 0;
-			rxe_run_task(&qp->req.task, 1);
+			rxe_run_task(&qp->req.task, 0);
 		}
 	}
 

@@ -725,7 +725,7 @@ int rxe_completer(void *arg)
 							RXE_CNT_COMP_RETRY);
 					qp->req.need_retry = 1;
 					qp->comp.started_retry = 1;
-					rxe_run_task(&qp->req.task, 1);
+					rxe_run_task(&qp->req.task, 0);
 				}
 
 				if (pkt) {