linux-kernel - [PATCH] IB/rdmavt: add lock to call to rvt_error

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Message-Id: <20220228165330.41546-1-dossche.niels@gmail.com>
Date:   Mon, 28 Feb 2022 17:53:30 +0100
From:   Niels Dossche <dossche.niels@...il.com>
To:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Mike Marciniszyn <mike.marciniszyn@...nelisnetworks.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Niels Dossche <dossche.niels@...il.com>
Subject: [PATCH] IB/rdmavt: add lock to call to rvt_error_qp to prevent a race condition

The documentation of the function rvt_error_qp says both r_lock and
s_lock need to be held when calling that function.
It also asserts using lockdep that both of those locks are held.
However, the commit I referenced in Fixes accidentally makes the call
to rvt_error_qp in rvt_ruc_loopback no longer covered by r_lock.
This results in the lockdep assertion failing and also possibly in a
race condition.

Fixes: d757c60eca9b ("IB/rdmavt: Fix concurrency panics in QP post_send and modify to error")
Signed-off-by: Niels Dossche <dossche.niels@...il.com>
---
 drivers/infiniband/sw/rdmavt/qp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/sw/rdmavt/qp.c b/drivers/infiniband/sw/rdmavt/qp.c
index ae50b56e8913..8ef112f883a7 100644
--- a/drivers/infiniband/sw/rdmavt/qp.c
+++ b/drivers/infiniband/sw/rdmavt/qp.c
@@ -3190,7 +3190,11 @@ void rvt_ruc_loopback(struct rvt_qp *sqp)
 	spin_lock_irqsave(&sqp->s_lock, flags);
 	rvt_send_complete(sqp, wqe, send_status);
 	if (sqp->ibqp.qp_type == IB_QPT_RC) {
-		int lastwqe = rvt_error_qp(sqp, IB_WC_WR_FLUSH_ERR);
+		int lastwqe;
+
+		spin_lock(&sqp->r_lock);
+		lastwqe = rvt_error_qp(sqp, IB_WC_WR_FLUSH_ERR);
+		spin_unlock(&sqp->r_lock);
 
 		sqp->s_flags &= ~RVT_S_BUSY;
 		spin_unlock_irqrestore(&sqp->s_lock, flags);
-- 
2.35.1