1 files changed, 46 insertions, 26 deletions

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 9b550ed..e8f046b 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -43,6 +43,7 @@
 #include <net/9p/client.h>
 #include <net/9p/transport.h>
 #include <linux/scatterlist.h>
+#include <linux/swap.h>
 #include <linux/virtio.h>
 #include <linux/virtio_9p.h>
 #include "trans_common.h"
@@ -51,6 +52,8 @@
 
 /* a single mutex to manage channel initialization and attachment */
 static DEFINE_MUTEX(virtio_9p_lock);
+static DECLARE_WAIT_QUEUE_HEAD(vp_wq);
+static atomic_t vp_pinned = ATOMIC_INIT(0);
 
 /**
  * struct virtio_chan - per-instance transport information
@@ -78,7 +81,10 @@ struct virtio_chan {
 	struct virtqueue *vq;
 	int ring_bufs_avail;
 	wait_queue_head_t *vc_wq;
-
+	/* This is global limit. Since we don't have a global structure,
+	 * will be placing it in each channel.
+	 */
+	int p9_max_pages;
 	/* Scatterlist: can be too big for stack. */
 	struct scatterlist sg[VIRTQUEUE_NUM];
 
@@ -141,34 +147,36 @@ static void req_done(struct virtqueue *vq)
 
 	P9_DPRINTK(P9_DEBUG_TRANS, ": request done\n");
 
-	do {
+	while (1) {
 		spin_lock_irqsave(&chan->lock, flags);
 		rc = virtqueue_get_buf(chan->vq, &len);
 
-		if (rc != NULL) {
-			if (!chan->ring_bufs_avail) {
-				chan->ring_bufs_avail = 1;
-				wake_up(chan->vc_wq);
-			}
-			spin_unlock_irqrestore(&chan->lock, flags);
-			P9_DPRINTK(P9_DEBUG_TRANS, ": rc %p\n", rc);
-			P9_DPRINTK(P9_DEBUG_TRANS, ": lookup tag %d\n",
-					rc->tag);
-			req = p9_tag_lookup(chan->client, rc->tag);
-			req->status = REQ_STATUS_RCVD;
-			if (req->tc->private) {
-				struct trans_rpage_info *rp = req->tc->private;
-				/*Release pages */
-				p9_release_req_pages(rp);
-				if (rp->rp_alloc)
-					kfree(rp);
-				req->tc->private = NULL;
-			}
-			p9_client_cb(chan->client, req);
-		} else {
+		if (rc == NULL) {
 			spin_unlock_irqrestore(&chan->lock, flags);
+			break;
+		}
+
+		chan->ring_bufs_avail = 1;
+		spin_unlock_irqrestore(&chan->lock, flags);
+		/* Wakeup if anyone waiting for VirtIO ring space. */
+		wake_up(chan->vc_wq);
+		P9_DPRINTK(P9_DEBUG_TRANS, ": rc %p\n", rc);
+		P9_DPRINTK(P9_DEBUG_TRANS, ": lookup tag %d\n", rc->tag);
+		req = p9_tag_lookup(chan->client, rc->tag);
+		if (req->tc->private) {
+			struct trans_rpage_info *rp = req->tc->private;
+			int p = rp->rp_nr_pages;
+			/*Release pages */
+			p9_release_req_pages(rp);
+			atomic_sub(p, &vp_pinned);
+			wake_up(&vp_wq);
+			if (rp->rp_alloc)
+				kfree(rp);
+			req->tc->private = NULL;
 		}
-	} while (rc != NULL);
+		req->status = REQ_STATUS_RCVD;
+		p9_client_cb(chan->client, req);
+	}
 }
 
 /**
@@ -263,7 +271,6 @@ p9_virtio_request(struct p9_client *client, struct p9_req_t *req)
 
 	P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio request\n");
 
-req_retry:
 	req->status = REQ_STATUS_SENT;
 
 	if (req->tc->pbuf_size && (req->tc->pubuf && P9_IS_USER_CONTEXT)) {
@@ -271,6 +278,14 @@ req_retry:
 		int rpinfo_size = sizeof(struct trans_rpage_info) +
 			sizeof(struct page *) * nr_pages;
 
+		if (atomic_read(&vp_pinned) >= chan->p9_max_pages) {
+			err = wait_event_interruptible(vp_wq,
+				atomic_read(&vp_pinned) < chan->p9_max_pages);
+			if (err  == -ERESTARTSYS)
+				return err;
+			P9_DPRINTK(P9_DEBUG_TRANS, "9p: May gup pages now.\n");
+		}
+
 		if (rpinfo_size <= (req->tc->capacity - req->tc->size)) {
 			/* We can use sdata */
 			req->tc->private = req->tc->sdata + req->tc->size;
@@ -293,9 +308,12 @@ req_retry:
 			if (rpinfo->rp_alloc)
 				kfree(rpinfo);
 			return err;
+		} else {
+			atomic_add(rpinfo->rp_nr_pages, &vp_pinned);
 		}
 	}
 
+req_retry_pinned:
 	spin_lock_irqsave(&chan->lock, flags);
 
 	/* Handle out VirtIO ring buffers */
@@ -356,7 +374,7 @@ req_retry:
 				return err;
 
 			P9_DPRINTK(P9_DEBUG_TRANS, "9p:Retry virtio request\n");
-			goto req_retry;
+			goto req_retry_pinned;
 		} else {
 			spin_unlock_irqrestore(&chan->lock, flags);
 			P9_DPRINTK(P9_DEBUG_TRANS,
@@ -453,6 +471,8 @@ static int p9_virtio_probe(struct virtio_device *vdev)
 	}
 	init_waitqueue_head(chan->vc_wq);
 	chan->ring_bufs_avail = 1;
+	/* Ceiling limit to avoid denial of service attacks */
+	chan->p9_max_pages = nr_free_buffer_pages()/4;
 
 	mutex_lock(&virtio_9p_lock);
 	list_add_tail(&chan->chan_list, &virtio_chan_list);