[PATCH v3 1/1] Add timer to handle OOM situations

[ggarcia]

From: Gerard Garcia <ggar...@deic.uab.cat>

v3:
 * Avoid race condition when freeing timer.

v2:
* Use of ERR_PTR/PTR_ERR/IS_ERR
* Timer cleaned on device release.
* Do not process more packets on error.

Signed-off-by: Gerard Garcia <ggar...@deic.uab.cat>
---
 drivers/vhost/vsock.c | 52 +++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 42 insertions(+), 10 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 028ca16..8d4fb13 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -15,11 +15,13 @@
 #include <net/sock.h>
 #include <linux/virtio_vsock.h>
 #include <linux/vhost.h>
+#include <linux/timer.h>
 
 #include <net/af_vsock.h>
 #include "vhost.h"
 
 #define VHOST_VSOCK_DEFAULT_HOST_CID   2
+#define OOM_RETRY_MS   100
 
 enum {
        VHOST_VSOCK_FEATURES = VHOST_FEATURES,
@@ -43,6 +45,8 @@ struct vhost_vsock {
        atomic_t queued_replies;
 
        u32 guest_cid;
+
+       struct timer_list tx_kick;
 };
 
 static u32 vhost_transport_get_local_cid(void)
@@ -229,12 +233,13 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
 
        if (in != 0) {
                vq_err(vq, "Expected 0 input buffers, got %u\n", in);
-               return NULL;
+               return ERR_PTR(-EINVAL);
        }
 
        pkt = kzalloc(sizeof(*pkt), GFP_KERNEL);
-       if (!pkt)
-               return NULL;
+       if (!pkt){
+               return ERR_PTR(-ENOMEM);
+       }
 
        len = iov_length(vq->iov, out);
        iov_iter_init(&iov_iter, WRITE, vq->iov, out, len);
@@ -244,7 +249,7 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
                vq_err(vq, "Expected %zu bytes for pkt->hdr, got %zu bytes\n",
                       sizeof(pkt->hdr), nbytes);
                kfree(pkt);
-               return NULL;
+               return ERR_PTR(-EINVAL);
        }
 
        if (le16_to_cpu(pkt->hdr.type) == VIRTIO_VSOCK_TYPE_STREAM)
@@ -257,13 +262,13 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
        /* The pkt is too big */
        if (pkt->len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) {
                kfree(pkt);
-               return NULL;
+               return ERR_PTR(-EINVAL);
        }
 
        pkt->buf = kmalloc(pkt->len, GFP_KERNEL);
        if (!pkt->buf) {
                kfree(pkt);
-               return NULL;
+               return ERR_PTR(-EINVAL);
        }
 
        nbytes = copy_from_iter(pkt->buf, pkt->len, &iov_iter);
@@ -271,7 +276,7 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
                vq_err(vq, "Expected %u byte payload, got %zu bytes\n",
                       pkt->len, nbytes);
                virtio_transport_free_pkt(pkt);
-               return NULL;
+               return ERR_PTR(-EINVAL);
        }
 
        return pkt;
@@ -329,9 +334,25 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work 
*work)
                }
 
                pkt = vhost_vsock_alloc_pkt(vq, out, in);
-               if (!pkt) {
-                       vq_err(vq, "Faulted on pkt\n");
-                       continue;
+               if (IS_ERR(pkt)) {
+                       if (PTR_ERR(pkt) == -ENOMEM) {
+                               vhost_discard_vq_desc(vq, 1);
+
+                               if (!timer_pending(&vsock->tx_kick)) {
+                                       vsock->tx_kick.data =
+                                               (unsigned long) vq;
+                                       vsock->tx_kick.expires =
+                                               jiffies + 
msecs_to_jiffies(OOM_RETRY_MS);
+                                       add_timer(&vsock->tx_kick);
+                               }
+
+                               break;
+                       } else {
+                               vq_err(vq, "Faulted on pkt\n");
+                               break;
+                       }
+               } else if (unlikely(timer_pending(&vsock->tx_kick))) {
+                       del_timer(&vsock->tx_kick);
                }
 
                /* Only accept correctly addressed packets */
@@ -352,6 +373,13 @@ out:
        mutex_unlock(&vq->mutex);
 }
 
+static void vhost_vsock_rehandle_tx_kick(unsigned long data)
+{
+       struct vhost_virtqueue *vq = (struct vhost_virtqueue *) data;
+
+       vhost_poll_queue(&vq->poll);
+}
+
 static void vhost_vsock_handle_rx_kick(struct vhost_work *work)
 {
        struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
@@ -464,6 +492,9 @@ static int vhost_vsock_dev_open(struct inode *inode, struct 
file *file)
 
        atomic_set(&vsock->queued_replies, 0);
 
+       setup_timer(&vsock->tx_kick,
+                   vhost_vsock_rehandle_tx_kick, (unsigned long) NULL);
+
        vqs[VSOCK_VQ_TX] = &vsock->vqs[VSOCK_VQ_TX];
        vqs[VSOCK_VQ_RX] = &vsock->vqs[VSOCK_VQ_RX];
        vsock->vqs[VSOCK_VQ_TX].handle_kick = vhost_vsock_handle_tx_kick;
@@ -527,6 +558,7 @@ static int vhost_vsock_dev_release(struct inode *inode, 
struct file *file)
        vsock_for_each_connected_socket(vhost_vsock_reset_orphans);
 
        vhost_vsock_stop(vsock);
+       del_timer_sync(&vsock->tx_kick);
        vhost_vsock_flush(vsock);
        vhost_dev_stop(&vsock->dev);
 
-- 
2.9.1