linux-kernel - [ 18/21] NTB: memcpy lockup workaround

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Message-Id: <20130522205234.722975333@linuxfoundation.org>
Date:	Wed, 22 May 2013 15:10:36 -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: [ 18/21] NTB: memcpy lockup workaround

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

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

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

commit c336acd3331dcc191a97dbc66a557d47741657c7 upstream.

The system will appear to lockup for long periods of time due to the NTB
driver spending too much time in memcpy.  Avoid this by reducing the
number of packets that can be serviced on a given interrupt.

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

---
 drivers/ntb/ntb_transport.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -1034,11 +1034,16 @@ out:
 static void ntb_transport_rx(unsigned long data)
 {
 	struct ntb_transport_qp *qp = (struct ntb_transport_qp *)data;
-	int rc;
+	int rc, i;
 
-	do {
+	/* Limit the number of packets processed in a single interrupt to
+	 * provide fairness to others
+	 */
+	for (i = 0; i < qp->rx_max_entry; i++) {
 		rc = ntb_process_rxc(qp);
-	} while (!rc);
+		if (rc)
+			break;
+	}
 }
 
 static void ntb_transport_rxc_db(void *data, int db_num)


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