linux-kernel - [ 17/21] NTB: Correctly handle receive buffers of the minimal size

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Message-Id: <20130522205234.618268643@linuxfoundation.org>
Date:	Wed, 22 May 2013 15:10:35 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Jon Mason <jon.mason@...el.com>
Subject: [ 17/21] NTB: Correctly handle receive buffers of the minimal size

3.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jon Mason <jon.mason@...el.com>

commit c9d534c8cbaedbb522a1d2cb037c6c394f610317 upstream.

The ring logic of the NTB receive buffer/transmit memory window requires
there to be at least 2 payload sized allotments.  For the minimal size
case, split the buffer into two and set the transport_mtu to the
appropriate size.

Signed-off-by: Jon Mason <jon.mason@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/ntb/ntb_transport.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -490,11 +490,12 @@ static void ntb_transport_setup_qp_mw(st
 	rx_size -= sizeof(struct ntb_rx_info);
 
 	qp->rx_buff = qp->remote_rx_info + 1;
-	qp->rx_max_frame = min(transport_mtu, rx_size);
+	/* Due to housekeeping, there must be atleast 2 buffs */
+	qp->rx_max_frame = min(transport_mtu, rx_size / 2);
 	qp->rx_max_entry = rx_size / qp->rx_max_frame;
 	qp->rx_index = 0;
 
-	qp->remote_rx_info->entry = qp->rx_max_entry;
+	qp->remote_rx_info->entry = qp->rx_max_entry - 1;
 
 	/* setup the hdr offsets with 0's */
 	for (i = 0; i < qp->rx_max_entry; i++) {
@@ -818,7 +819,8 @@ static void ntb_transport_init_queue(str
 	tx_size -= sizeof(struct ntb_rx_info);
 
 	qp->tx_mw = qp->rx_info + 1;
-	qp->tx_max_frame = min(transport_mtu, tx_size);
+	/* Due to housekeeping, there must be atleast 2 buffs */
+	qp->tx_max_frame = min(transport_mtu, tx_size / 2);
 	qp->tx_max_entry = tx_size / qp->tx_max_frame;
 
 	if (nt->debugfs_dir) {


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