Currently, vs->vs_endpoint is used indicate if the endpoint is setup or
not. It is set or cleared in vhost_scsi_set_endpoint() or
vhost_scsi_clear_endpoint() under the vs->dev.mutex lock. However, when
we check it in vhost_scsi_handle_vq(), we ignored the lock.
Instead of using the vs->vs_endpoint and the vs->dev.mutex lock to
indicate the status of the endpoint, we use per virtqueue
vq->private_data to indicate it. In this way, we can only take the
vq->mutex lock which is per queue and make the concurrent multiqueue
process having less lock contention. Further, in the read side of
vq->private_data, we can even do not take the lock if it is accessed in
the vhost worker thread, because it is protected by "vhost rcu".
Signed-off-by: Asias He <asias@xxxxxxxxxx>
---
drivers/vhost/tcm_vhost.c | 144 ++++++++++++++++++++++++++++++++--------------
1 file changed, 101 insertions(+), 43 deletions(-)
diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
index 61f9eab..11121ea 100644
--- a/drivers/vhost/tcm_vhost.c
+++ b/drivers/vhost/tcm_vhost.c
@@ -65,9 +65,8 @@ enum {
struct vhost_scsi {
/* Protected by vhost_scsi->dev.mutex */
- struct tcm_vhost_tpg *vs_tpg[VHOST_SCSI_MAX_TARGET];
+ struct tcm_vhost_tpg **vs_tpg;
char vs_vhost_wwpn[TRANSPORT_IQN_LEN];
- bool vs_endpoint;
struct vhost_dev dev;
struct vhost_virtqueue vqs[VHOST_SCSI_MAX_VQ];
@@ -573,6 +572,7 @@ static void tcm_vhost_submission_work(struct work_struct *work)
static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
struct vhost_virtqueue *vq)
{
+ struct tcm_vhost_tpg **vs_tpg;
struct virtio_scsi_cmd_req v_req;
struct tcm_vhost_tpg *tv_tpg;
struct tcm_vhost_cmd *tv_cmd;
@@ -581,8 +581,16 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
int head, ret;
u8 target;
- /* Must use ioctl VHOST_SCSI_SET_ENDPOINT */
- if (unlikely(!vs->vs_endpoint))
+ /*
+ * We can handle the vq only after the endpoint is setup by calling the
+ * VHOST_SCSI_SET_ENDPOINT ioctl.
+ *
+ * TODO: Check that we are running from vhost_worker which acts
+ * as read-side critical section for vhost kind of RCU.
+ * See the comments in struct vhost_virtqueue in drivers/vhost/vhost.h
+ */
+ vs_tpg = rcu_dereference_check(vq->private_data, 1);
+ if (!vs_tpg)
return;
mutex_lock(&vq->mutex);
@@ -652,7 +660,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
/* Extract the tpgt */
target = v_req.lun[1];
- tv_tpg = ACCESS_ONCE(vs->vs_tpg[target]);
+ tv_tpg = ACCESS_ONCE(vs_tpg[target]);
/* Target does not exist, fail the request */
if (unlikely(!tv_tpg)) {
@@ -771,6 +779,20 @@ static void vhost_scsi_handle_kick(struct vhost_work *work)
vhost_scsi_handle_vq(vs, vq);
}
+static void vhost_scsi_flush_vq(struct vhost_scsi *vs, int index)
+{
+ vhost_poll_flush(&vs->dev.vqs[index].poll);
+}
+
+static void vhost_scsi_flush(struct vhost_scsi *vs)
+{
+ int i;
+
+ for (i = 0; i < VHOST_SCSI_MAX_VQ; i++)
+ vhost_scsi_flush_vq(vs, i);
+ vhost_work_flush(&vs->dev, &vs->vs_completion_work);
+}
+
/*
* Called from vhost_scsi_ioctl() context to walk the list of available
* tcm_vhost_tpg with an active struct tcm_vhost_nexus
@@ -781,8 +803,10 @@ static int vhost_scsi_set_endpoint(
{
struct tcm_vhost_tport *tv_tport;
struct tcm_vhost_tpg *tv_tpg;
+ struct tcm_vhost_tpg **vs_tpg;
+ struct vhost_virtqueue *vq;
+ int index, ret, i, len;
bool match = false;
- int index, ret;
mutex_lock(&vs->dev.mutex);
/* Verify that ring has been setup correctly. */
@@ -794,6 +818,15 @@ static int vhost_scsi_set_endpoint(
}
}
+ len = sizeof(vs_tpg[0]) * VHOST_SCSI_MAX_TARGET;
+ vs_tpg = kzalloc(len, GFP_KERNEL);
+ if (!vs_tpg) {
+ mutex_unlock(&vs->dev.mutex);
+ return -ENOMEM;
+ }
+ if (vs->vs_tpg)
+ memcpy(vs_tpg, vs->vs_tpg, len);
+
mutex_lock(&tcm_vhost_mutex);
list_for_each_entry(tv_tpg, &tcm_vhost_list, tv_tpg_list) {
mutex_lock(&tv_tpg->tv_tpg_mutex);
@@ -808,14 +841,15 @@ static int vhost_scsi_set_endpoint(
tv_tport = tv_tpg->tport;
if (!strcmp(tv_tport->tport_name, t->vhost_wwpn)) {
- if (vs->vs_tpg[tv_tpg->tport_tpgt]) {
+ if (vs->vs_tpg && vs->vs_tpg[tv_tpg->tport_tpgt]) {
mutex_unlock(&tv_tpg->tv_tpg_mutex);
mutex_unlock(&tcm_vhost_mutex);
mutex_unlock(&vs->dev.mutex);
+ kfree(vs_tpg);
return -EEXIST;
}
tv_tpg->tv_tpg_vhost_count++;
- vs->vs_tpg[tv_tpg->tport_tpgt] = tv_tpg;
+ vs_tpg[tv_tpg->tport_tpgt] = tv_tpg;
smp_mb__after_atomic_inc();
match = true;
}
@@ -826,12 +860,26 @@ static int vhost_scsi_set_endpoint(
if (match) {
memcpy(vs->vs_vhost_wwpn, t->vhost_wwpn,
sizeof(vs->vs_vhost_wwpn));
- vs->vs_endpoint = true;
+ for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) {
+ vq = &vs->vqs[i];
+ /* Flushing the vhost_work acts as synchronize_rcu */
+ mutex_lock(&vq->mutex);
+ rcu_assign_pointer(vq->private_data, vs_tpg);
+ mutex_unlock(&vq->mutex);
+ }
ret = 0;
} else {
ret = -EEXIST;
}
+ /*
+ * Act as synchronize_rcu to make sure access to
+ * old vs->vs_tpg is finished.
+ */
+ vhost_scsi_flush(vs);
+ kfree(vs->vs_tpg);
+ vs->vs_tpg = vs_tpg;
+
mutex_unlock(&vs->dev.mutex);
return ret;
}
@@ -842,6 +890,8 @@ static int vhost_scsi_clear_endpoint(
{
struct tcm_vhost_tport *tv_tport;
struct tcm_vhost_tpg *tv_tpg;
+ struct vhost_virtqueue *vq;
+ bool match = false;
int index, ret, i;
u8 target;
@@ -853,9 +903,14 @@ static int vhost_scsi_clear_endpoint(
goto err_dev;
}
}
+
+ if (!vs->vs_tpg) {
+ mutex_unlock(&vs->dev.mutex);
+ return 0;
+ }
+
for (i = 0; i < VHOST_SCSI_MAX_TARGET; i++) {
target = i;
-
tv_tpg = vs->vs_tpg[target];
if (!tv_tpg)
continue;
@@ -877,10 +932,27 @@ static int vhost_scsi_clear_endpoint(
}
tv_tpg->tv_tpg_vhost_count--;
vs->vs_tpg[target] = NULL;
- vs->vs_endpoint = false;
+ match = true;
mutex_unlock(&tv_tpg->tv_tpg_mutex);
}
+ if (match) {
+ for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) {
+ vq = &vs->vqs[i];
+ /* Flushing the vhost_work acts as synchronize_rcu */
+ mutex_lock(&vq->mutex);
+ rcu_assign_pointer(vq->private_data, NULL);
+ mutex_unlock(&vq->mutex);
+ }
+ }
+ /*
+ * Act as synchronize_rcu to make sure access to
+ * old vs->vs_tpg is finished.
+ */
+ vhost_scsi_flush(vs);
+ kfree(vs->vs_tpg);
+ vs->vs_tpg = NULL;
mutex_unlock(&vs->dev.mutex);
+
return 0;
err_tpg:
@@ -890,6 +962,24 @@ err_dev:
return ret;
}
+static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
+{
+ if (features & ~VHOST_FEATURES)
+ return -EOPNOTSUPP;
+
+ mutex_lock(&vs->dev.mutex);
+ if ((features & (1 << VHOST_F_LOG_ALL)) &&
+ !vhost_log_access_ok(&vs->dev)) {
+ mutex_unlock(&vs->dev.mutex);
+ return -EFAULT;
+ }
+ vs->dev.acked_features = features;
+ smp_wmb();
+ vhost_scsi_flush(vs);
+ mutex_unlock(&vs->dev.mutex);
+ return 0;
+}
+
static int vhost_scsi_open(struct inode *inode, struct file *f)
{
struct vhost_scsi *s;
@@ -930,38 +1020,6 @@ static int vhost_scsi_release(struct inode *inode, struct file *f)
return 0;
}
-static void vhost_scsi_flush_vq(struct vhost_scsi *vs, int index)
-{
- vhost_poll_flush(&vs->dev.vqs[index].poll);
-}
-
-static void vhost_scsi_flush(struct vhost_scsi *vs)
-{
- int i;
-
- for (i = 0; i < VHOST_SCSI_MAX_VQ; i++)
- vhost_scsi_flush_vq(vs, i);
- vhost_work_flush(&vs->dev, &vs->vs_completion_work);
-}
-
-static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
-{
- if (features & ~VHOST_FEATURES)
- return -EOPNOTSUPP;
-
- mutex_lock(&vs->dev.mutex);
- if ((features & (1 << VHOST_F_LOG_ALL)) &&
- !vhost_log_access_ok(&vs->dev)) {
- mutex_unlock(&vs->dev.mutex);
- return -EFAULT;
- }
- vs->dev.acked_features = features;
- smp_wmb();
- vhost_scsi_flush(vs);
- mutex_unlock(&vs->dev.mutex);
- return 0;
-}
-
static long vhost_scsi_ioctl(struct file *f, unsigned int ioctl,
unsigned long arg)
{
--
1.8.1.4
--
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