[ofa-general] [PATCH] IB/mlx4: Fix race when detaching a QP from a MCG

[Eli Cohen]

>From 9c725ff918d026e2765e053e5f09c51ee82e0282 Mon Sep 17 00:00:00 2001
From: Eli Cohen <eli at mellanox.co.il>
Date: Thu, 10 Apr 2008 11:47:54 +0300
Subject: [PATCH] IB/mlx4: Fix race when detaching a QP from a MCG

When detaching the last QP from an MCG entry, we need to make
sure that at any time, there will be no entry with zero number of
QPs which is linked to the list of the MCGs of the corresponding
hash index.

Also, it removes an unnecessary MCG read when attaching a QP requires
allocation of a new entry in the AMGM.

Signed-off-by: Eli Cohen <eli at mellanox.co.il>
Found by: Mellanox regression team
---
 drivers/net/mlx4/mcg.c |   12 +++---------
 1 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/drivers/net/mlx4/mcg.c b/drivers/net/mlx4/mcg.c
index a99e772..57f7f1f 100644
--- a/drivers/net/mlx4/mcg.c
+++ b/drivers/net/mlx4/mcg.c
@@ -190,10 +190,6 @@ int mlx4_multicast_attach(struct mlx4_dev *dev, struct mlx4_qp *qp, u8 gid[16])
 		}
 		index += dev->caps.num_mgms;
 
-		err = mlx4_READ_MCG(dev, index, mailbox);
-		if (err)
-			goto out;
-
 		memset(mgm, 0, sizeof *mgm);
 		memcpy(mgm->gid, gid, 16);
 	}
@@ -301,12 +297,10 @@ int mlx4_multicast_detach(struct mlx4_dev *dev, struct mlx4_qp *qp, u8 gid[16])
 	mgm->qp[loc]       = mgm->qp[i - 1];
 	mgm->qp[i - 1]     = 0;
 
-	err = mlx4_WRITE_MCG(dev, index, mailbox);
-	if (err)
-		goto out;
-
-	if (i != 1)
+	if (i != 1) {
+		err = mlx4_WRITE_MCG(dev, index, mailbox);
 		goto out;
+	}
 
 	if (prev == -1) {
 		/* Remove entry from MGM */
-- 
1.5.5