Commit 7a3246bf authored by Liu Xiaodong's avatar Liu Xiaodong Committed by Jim Harris
Browse files

vhost: fetch and check avail_idx from memory 



Since there may be race condition, num_events gotten
from kickfd is not always right to reflect the number
of requests in virtqueue. So remove this check.
Instead, avail_idx in memory reflects the real situation
whether there is unprocessed requests in queue.

Change-Id: I4e59242cf3101ece912777533411bc4dcdc81c9d
Signed-off-by: default avatarLiu Xiaodong <xiaodong.liu@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/5787


Tested-by: default avatarSPDK CI Jenkins <sys_sgci@intel.com>
Community-CI: Mellanox Build Bot
Reviewed-by: default avatarChangpeng Liu <changpeng.liu@intel.com>
Reviewed-by: default avatarJim Harris <james.r.harris@intel.com>
parent fce2956c

lib/vhost/vhost.c

+13 −16
Original line number Diff line number Diff line
@@ -184,23 +184,17 @@ vhost_vq_avail_ring_get(struct spdk_vhost_virtqueue *virtqueue, uint16_t *reqs, 
	uint16_t last_idx = virtqueue->last_avail_idx, avail_idx = avail->idx;

	uint16_t count, i;

	int rc;

	uint64_t num_events;

	uint64_t u64_value;



	spdk_smp_rmb();



	if (virtqueue->vsession && spdk_unlikely(virtqueue->vsession->interrupt_mode)) {

		/* Acknowledge vring's kickfd */

		rc = read(vring->kickfd, &num_events, sizeof(num_events));

		/* Read to clear vring's kickfd */

		rc = read(vring->kickfd, &u64_value, sizeof(u64_value));

		if (rc < 0) {

			SPDK_ERRLOG("failed to acknowledge kickfd: %s.\n", spdk_strerror(errno));

			return -errno;

		}



		if ((uint16_t)(avail_idx - last_idx) != num_events) {

			SPDK_DEBUGLOG(vhost_ring,

				      "virtqueue gets %d reqs, but kickfd shows %lu reqs\n",

				      avail_idx - last_idx, num_events);

		}

	}



	count = avail_idx - last_idx;
@@ -216,13 +210,17 @@ vhost_vq_avail_ring_get(struct spdk_vhost_virtqueue *virtqueue, uint16_t *reqs, 
	}



	count = spdk_min(count, reqs_len);



	virtqueue->last_avail_idx += count;

	/* Check whether there are unprocessed reqs in vq, then kick vq manually */

	if (virtqueue->vsession && spdk_unlikely(virtqueue->vsession->interrupt_mode)) {

		if (num_events > count) {

			SPDK_DEBUGLOG(vhost_ring,

				      "virtqueue kickfd shows %lu reqs, take %d, send notice for other reqs\n",

				      num_events, reqs_len);

			num_events -= count;

			rc = write(vring->kickfd, &num_events, sizeof(num_events));

		/* If avail_idx is larger than virtqueue's last_avail_idx, then there is unprocessed reqs.

		 * avail_idx should get updated here from memory, in case of race condition with guest.

		 */

		avail_idx = * (volatile uint16_t *) &avail->idx;

		if (avail_idx > virtqueue->last_avail_idx) {

			/* Write to notify vring's kickfd */

			rc = write(vring->kickfd, &u64_value, sizeof(u64_value));

			if (rc < 0) {

				SPDK_ERRLOG("failed to kick vring: %s.\n", spdk_strerror(errno));

				return -errno;
@@ -230,7 +228,6 @@ vhost_vq_avail_ring_get(struct spdk_vhost_virtqueue *virtqueue, uint16_t *reqs, 
		}

	}



	virtqueue->last_avail_idx += count;

	for (i = 0; i < count; i++) {

		reqs[i] = vring->avail->ring[(last_idx + i) & size_mask];

	}