From mboxrd@z Thu Jan  1 00:00:00 1970
From: Zhu Yanjun <yanjun.zhu@oracle.com>
Subject: [PATCHv2 1/1] net/mlx4_core: avoid resetting HCA when accessing an  offline device
Date: Wed, 18 Apr 2018 09:31:43 -0400
Message-ID: <1524058303-379-1-git-send-email-yanjun.zhu@oracle.com>
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Return-path: <netdev-owner@vger.kernel.org>
Sender: netdev-owner@vger.kernel.org
To: tariqt@mellanox.com, netdev@vger.kernel.org, linux-rdma@vger.kernel.org
List-Id: linux-rdma@vger.kernel.org

While a faulty cable is used or HCA firmware error, HCA device will
be offline. When the driver is accessing this offline device, the
following call trace will pop out.

"
...
  [<ffffffff816e4842>] dump_stack+0x63/0x81
  [<ffffffff816e459e>] panic+0xcc/0x21b
  [<ffffffffa03e5f8a>] mlx4_enter_error_state+0xba/0xf0 [mlx4_core]
  [<ffffffffa03e7298>] mlx4_cmd_reset_flow+0x38/0x60 [mlx4_core]
  [<ffffffffa03e7381>] mlx4_cmd_poll+0xc1/0x2e0 [mlx4_core]
  [<ffffffffa03e9f00>] __mlx4_cmd+0xb0/0x160 [mlx4_core]
  [<ffffffffa0406934>] mlx4_SENSE_PORT+0x54/0xd0 [mlx4_core]
  [<ffffffffa03f5f54>] mlx4_dev_cap+0x4a4/0xb50 [mlx4_core]
...
"
In the above call trace, the function mlx4_cmd_poll calls the function
mlx4_cmd_post to access the HCA while HCA is offline. Then mlx4_cmd_post
returns an error -EIO. Per -EIO, the function mlx4_cmd_poll calls
mlx4_cmd_reset_flow to reset HCA. And the above call trace pops out.

This is not reasonable. Since HCA device is offline when it is being
accessed, it should not be reset again.

In this patch, since HCA is offline, the function mlx4_cmd_post returns
an error -EINVAL. Per -EINVAL, the function mlx4_cmd_poll directly returns
instead of resetting HCA.

CC: Srinivas Eeda <srinivas.eeda@oracle.com>
CC: Junxiao Bi <junxiao.bi@oracle.com>
Suggested-by: Håkon Bugge <haakon.bugge@oracle.com>
Suggested-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Zhu Yanjun <yanjun.zhu@oracle.com>
---
V1->V2: Follow Tariq's advice, avoid the disturbance from other returned errors.
Since the returned values from the function mlx4_cmd_post are -EIO and -EINVAL,
to -EIO, the HCA device should be reset. To -EINVAL, that means that the function
mlx4_cmd_post is accessing an offline device. It is not necessary to reset HCA.
Go to label out directly.
---
 drivers/net/ethernet/mellanox/mlx4/cmd.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/cmd.c b/drivers/net/ethernet/mellanox/mlx4/cmd.c
index 6a9086d..df735b8 100644
--- a/drivers/net/ethernet/mellanox/mlx4/cmd.c
+++ b/drivers/net/ethernet/mellanox/mlx4/cmd.c
@@ -451,6 +451,8 @@ static int mlx4_cmd_post(struct mlx4_dev *dev, u64 in_param, u64 out_param,
 		 * Device is going through error recovery
 		 * and cannot accept commands.
 		 */
+		mlx4_err(dev, "%s : Device is in error recovery.\n", __func__);
+		ret = -EINVAL;
 		goto out;
 	}
 
@@ -610,8 +612,11 @@ static int mlx4_cmd_poll(struct mlx4_dev *dev, u64 in_param, u64 *out_param,
 
 	err = mlx4_cmd_post(dev, in_param, out_param ? *out_param : 0,
 			    in_modifier, op_modifier, op, CMD_POLL_TOKEN, 0);
-	if (err)
+	if (err) {
+		if (err == -EINVAL)
+			goto out;
 		goto out_reset;
+	}
 
 	end = msecs_to_jiffies(timeout) + jiffies;
 	while (cmd_pending(dev) && time_before(jiffies, end)) {
@@ -710,8 +715,11 @@ static int mlx4_cmd_wait(struct mlx4_dev *dev, u64 in_param, u64 *out_param,
 
 	err = mlx4_cmd_post(dev, in_param, out_param ? *out_param : 0,
 			    in_modifier, op_modifier, op, context->token, 1);
-	if (err)
+	if (err) {
+		if (err == -EINVAL)
+			goto out;
 		goto out_reset;
+	}
 
 	if (op == MLX4_CMD_SENSE_PORT) {
 		ret_wait =
-- 
2.7.4