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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Zhu Yanjun <yanjunz@mellanox.com>,
        Leon Romanovsky <leonro@mellanox.com>,
        Jason Gunthorpe <jgg@mellanox.com>
Subject: [PATCH 5.5 56/80] RDMA/rxe: Fix soft lockup problem due to using tasklets in softirq
Date:   Tue, 18 Feb 2020 20:55:17 +0100
Message-Id: <20200218190437.492485814@linuxfoundation.org>
In-Reply-To: <20200218190432.043414522@linuxfoundation.org>
References: <20200218190432.043414522@linuxfoundation.org>
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From: Zhu Yanjun <yanjunz@mellanox.com>

commit 8ac0e6641c7ca14833a2a8c6f13d8e0a435e535c upstream.

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".

Fixes: 8700e3e7c485 ("Soft RoCE driver")
Link: https://lore.kernel.org/r/20200212072635.682689-8-leon@kernel.org
Signed-off-by: Zhu Yanjun <yanjunz@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/infiniband/sw/rxe/rxe_comp.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/infiniband/sw/rxe/rxe_comp.c
+++ b/drivers/infiniband/sw/rxe/rxe_comp.c
@@ -329,7 +329,7 @@ static inline enum comp_state check_ack(
 					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 *q
 	 */
 	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_a
 		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) {