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tcm_vhost: Use vq->private_data to indicate if the endpoint is setup
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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".

(nab: Do s/VHOST_FEATURES/~VHOST_SCSI_FEATURES)

Signed-off-by: Asias He <asias@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
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Asias He authored and Nicholas Bellinger committed Apr 8, 2013
1 parent af0d918 commit 4f7f46d
Showing 1 changed file with 101 additions and 43 deletions.
144 changes: 101 additions & 43 deletions drivers/vhost/tcm_vhost.c
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Original file line number Diff line number Diff line change
Expand Up @@ -74,9 +74,8 @@ 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];
Expand Down Expand Up @@ -582,6 +581,7 @@ 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;
Expand All @@ -590,8 +590,16 @@ 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);
Expand Down Expand Up @@ -661,7 +669,7 @@ 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)) {
Expand Down Expand Up @@ -780,6 +788,20 @@ 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
Expand All @@ -790,8 +812,10 @@ 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. */
Expand All @@ -803,6 +827,15 @@ 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);
Expand All @@ -817,14 +850,15 @@ 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;
}
Expand All @@ -835,12 +869,26 @@ 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;
}
Expand All @@ -851,6 +899,8 @@ 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;

Expand All @@ -862,9 +912,14 @@ 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;
Expand All @@ -886,10 +941,27 @@ 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:
Expand All @@ -899,6 +971,24 @@ static int vhost_scsi_clear_endpoint(
return ret;
}

static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
{
if (features & ~VHOST_SCSI_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;
Expand Down Expand Up @@ -939,38 +1029,6 @@ 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_SCSI_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)
{
Expand Down

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