linux-kernel - [PATCH 5.15 449/779] RDMA/rxe: Fix deadlock in rxe_do_local

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Date:   Mon, 15 Aug 2022 20:01:33 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jenny Hack <jhack@....com>,
        Bob Pearson <rpearsonhpe@...il.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 449/779] RDMA/rxe: Fix deadlock in rxe_do_local_ops()

From: Bob Pearson <rpearsonhpe@...il.com>

[ Upstream commit 7cb33d1bc1ac8e51fd88928f96674d392f8e07c4 ]

When a local operation (invalidate mr, reg mr, bind mw) is finished there
will be no ack packet coming from a responder to cause the wqe to be
completed. This may happen anyway if a subsequent wqe performs
IO. Currently if the wqe is signalled the completer tasklet is scheduled
immediately but not otherwise.

This leads to a deadlock if the next wqe has the fence bit set in send
flags and the operation is not signalled. This patch removes the condition
that the wqe must be signalled in order to schedule the completer tasklet
which is the simplest fix for this deadlock and is fairly low cost. This
is the analog for local operations of always setting the ackreq bit in all
last or only request packets even if the operation is not signalled.

Link: https://lore.kernel.org/r/20220523223251.15350-1-rpearsonhpe@gmail.com
Reported-by: Jenny Hack <jhack@....com>
Fixes: c1a411268a4b ("RDMA/rxe: Move local ops to subroutine")
Signed-off-by: Bob Pearson <rpearsonhpe@...il.com>
Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/infiniband/sw/rxe/rxe_req.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_req.c b/drivers/infiniband/sw/rxe/rxe_req.c
index 7812e3d6a6c2..4ea9319f0d52 100644
--- a/drivers/infiniband/sw/rxe/rxe_req.c
+++ b/drivers/infiniband/sw/rxe/rxe_req.c
@@ -612,9 +612,11 @@ static int rxe_do_local_ops(struct rxe_qp *qp, struct rxe_send_wqe *wqe)
 	wqe->status = IB_WC_SUCCESS;
 	qp->req.wqe_index = next_index(qp->sq.queue, qp->req.wqe_index);

-	if ((wqe->wr.send_flags & IB_SEND_SIGNALED) ||
-	    qp->sq_sig_type == IB_SIGNAL_ALL_WR)
-		rxe_run_task(&qp->comp.task, 1);
+	/* There is no ack coming for local work requests
+	 * which can lead to a deadlock. So go ahead and complete
+	 * it now.
+	 */
+	rxe_run_task(&qp->comp.task, 1);

 	return 0;
 }
-- 
2.35.1