Hi MST & Co,
Quick question below wrt to this patch..
On Thu, 2014-10-09 at 03:34 +0000, Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
>
> This patch addresses a bug where individual vhost-scsi configfs endpoint
> groups can be removed from below while active exports to QEMU userspace
> still exist, resulting in an OOPs.
>
> It adds a configfs_depend_item() in vhost_scsi_set_endpoint() to obtain
> an explicit dependency on se_tpg->tpg_group in order to prevent individual
> vhost-scsi WWPN endpoints from being released via normal configfs methods
> while an QEMU ioctl reference still exists.
>
> Also, add matching configfs_undepend_item() in vhost_scsi_clear_endpoint()
> to release the dependency, once QEMU's reference to the individual group
> at /sys/kernel/config/target/vhost/$WWPN/$TPGT is released.
>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # 3.6+
> Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
> ---
> drivers/vhost/scsi.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> index 69906ca..bc1b620 100644
> --- a/drivers/vhost/scsi.c
> +++ b/drivers/vhost/scsi.c
> @@ -1312,6 +1312,7 @@ static int
> vhost_scsi_set_endpoint(struct vhost_scsi *vs,
> struct vhost_scsi_target *t)
> {
> + struct se_portal_group *se_tpg;
> struct tcm_vhost_tport *tv_tport;
> struct tcm_vhost_tpg *tpg;
> struct tcm_vhost_tpg **vs_tpg;
> @@ -1359,6 +1360,19 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
> ret = -EEXIST;
> goto out;
> }
> + /*
> + * In order to ensure individual vhost-scsi configfs
> + * groups cannot be removed while in use by vhost ioctl,
> + * go ahead and take an explicit se_tpg->tpg_group.cg_item
> + * dependency now.
> + */
> + se_tpg = &tpg->se_tpg;
> + ret = configfs_depend_item(se_tpg->se_tpg_tfo->tf_subsys,
> + &se_tpg->tpg_group.cg_item);
> + if (ret) {
> + pr_warn("configfs_depend_item() failed: %d\n", ret);
> + goto out;
> + }
> tpg->tv_tpg_vhost_count++;
> tpg->vhost_scsi = vs;
> vs_tpg[tpg->tport_tpgt] = tpg;
> @@ -1401,6 +1415,7 @@ static int
> vhost_scsi_clear_endpoint(struct vhost_scsi *vs,
> struct vhost_scsi_target *t)
> {
> + struct se_portal_group *se_tpg;
> struct tcm_vhost_tport *tv_tport;
> struct tcm_vhost_tpg *tpg;
> struct vhost_virtqueue *vq;
> @@ -1449,6 +1464,13 @@ vhost_scsi_clear_endpoint(struct vhost_scsi *vs,
> vs->vs_tpg[target] = NULL;
> match = true;
> mutex_unlock(&tpg->tv_tpg_mutex);
> + /*
> + * Release se_tpg->tpg_group.cg_item configfs dependency now
> + * to allow vhost-scsi WWPN se_tpg->tpg_group shutdown to occur.
> + */
> + se_tpg = &tpg->se_tpg;
> + configfs_undepend_item(se_tpg->se_tpg_tfo->tf_subsys,
> + &se_tpg->tpg_group.cg_item);
> }
> if (match) {
> for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) {
AFAICT from qemu code, the ioctl VHOST_SCSI_CLEAR_ENDPOINT is always
called during shutdown in order to release the endpoint and drop this
new configfs dependency.
The question is, what happens when qemu crashes..? Is there currently
an assurance that VHOST_SCSI_CLEAR_ENDPOINT is called via the normal
VirtioDeviceClass->unrealize() when qemu exits abnormally..?
Thanks,
--nab
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