[PATCH 4.4 40/58] xen-netback: correctly schedule rate-limited queues - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Jean-Louis Dupond <jean-louis@dupond.be>,
	Wei Liu <wei.liu2@citrix.com>,
	Paul Durrant <paul.durrant@citrix.com>,
	"David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.4 40/58] xen-netback: correctly schedule rate-limited queues
Date: Wed,  9 Aug 2017 12:41:52 -0700	[thread overview]
Message-ID: <20170809194148.090871966@linuxfoundation.org> (raw)
In-Reply-To: <20170809194146.501519882@linuxfoundation.org>

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

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

From: Wei Liu <wei.liu2@citrix.com>


[ Upstream commit dfa523ae9f2542bee4cddaea37b3be3e157f6e6b ]

Add a flag to indicate if a queue is rate-limited. Test the flag in
NAPI poll handler and avoid rescheduling the queue if true, otherwise
we risk locking up the host. The rescheduling will be done in the
timer callback function.

Reported-by: Jean-Louis Dupond <jean-louis@dupond.be>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Tested-by: Jean-Louis Dupond <jean-louis@dupond.be>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/xen-netback/common.h    |    1 +
 drivers/net/xen-netback/interface.c |    6 +++++-
 drivers/net/xen-netback/netback.c   |    6 +++++-
 3 files changed, 11 insertions(+), 2 deletions(-)

--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -201,6 +201,7 @@ struct xenvif_queue { /* Per-queue data
 	unsigned long   remaining_credit;
 	struct timer_list credit_timeout;
 	u64 credit_window_start;
+	bool rate_limited;
 
 	/* Statistics */
 	struct xenvif_stats stats;
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -105,7 +105,11 @@ static int xenvif_poll(struct napi_struc
 
 	if (work_done < budget) {
 		napi_complete(napi);
-		xenvif_napi_schedule_or_enable_events(queue);
+		/* If the queue is rate-limited, it shall be
+		 * rescheduled in the timer callback.
+		 */
+		if (likely(!queue->rate_limited))
+			xenvif_napi_schedule_or_enable_events(queue);
 	}
 
 	return work_done;
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -687,6 +687,7 @@ static void tx_add_credit(struct xenvif_
 		max_credit = ULONG_MAX; /* wrapped: clamp to ULONG_MAX */
 
 	queue->remaining_credit = min(max_credit, max_burst);
+	queue->rate_limited = false;
 }
 
 void xenvif_tx_credit_callback(unsigned long data)
@@ -1184,8 +1185,10 @@ static bool tx_credit_exceeded(struct xe
 		msecs_to_jiffies(queue->credit_usec / 1000);
 
 	/* Timer could already be pending in rare cases. */
-	if (timer_pending(&queue->credit_timeout))
+	if (timer_pending(&queue->credit_timeout)) {
+		queue->rate_limited = true;
 		return true;
+	}
 
 	/* Passed the point where we can replenish credit? */
 	if (time_after_eq64(now, next_credit)) {
@@ -1200,6 +1203,7 @@ static bool tx_credit_exceeded(struct xe
 		mod_timer(&queue->credit_timeout,
 			  next_credit);
 		queue->credit_window_start = next_credit;
+		queue->rate_limited = true;
 
 		return true;
 	}
