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From: Mike Christie <michael.christie@oracle.com>
To: martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
	target-devel@vger.kernel.org, mst@redhat.com,
	jasowang@redhat.com, pbonzini@redhat.com, stefanha@redhat.com,
	virtualization@lists.linux-foundation.org
Subject: [PATCH 4/8] vhost scsi: fix cmd completion race
Date: Mon, 21 Sep 2020 13:23:04 -0500
Message-ID: <1600712588-9514-5-git-send-email-michael.christie@oracle.com> (raw)
In-Reply-To: <1600712588-9514-1-git-send-email-michael.christie@oracle.com>

We might not do the final se_cmd put from vhost_scsi_complete_cmd_work.
If the last put happens a little later then we could race where
vhost_scsi_complete_cmd_work does vhost_signal, the guest runs and sends
more IO, and vhost_scsi_handle_vq runs but does not find any free cmds.

This patch has us delay completing the cmd until the last lio core ref
is dropped. We then know that once we signal to the guest that the cmd
is completed that if it queues a new command it will find a free cmd.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
---
 drivers/vhost/scsi.c | 42 +++++++++++++++---------------------------
 1 file changed, 15 insertions(+), 27 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 13311b8..26d0f75 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -322,7 +322,7 @@ static u32 vhost_scsi_tpg_get_inst_index(struct se_portal_group *se_tpg)
 	return 1;
 }
 
-static void vhost_scsi_release_cmd(struct se_cmd *se_cmd)
+static void vhost_scsi_release_cmd_res(struct se_cmd *se_cmd)
 {
 	struct vhost_scsi_cmd *tv_cmd = container_of(se_cmd,
 				struct vhost_scsi_cmd, tvc_se_cmd);
@@ -344,6 +344,16 @@ static void vhost_scsi_release_cmd(struct se_cmd *se_cmd)
 	vhost_scsi_put_inflight(inflight);
 }
 
+static void vhost_scsi_release_cmd(struct se_cmd *se_cmd)
+{
+	struct vhost_scsi_cmd *cmd = container_of(se_cmd,
+					struct vhost_scsi_cmd, tvc_se_cmd);
+	struct vhost_scsi *vs = cmd->tvc_vhost;
+
+	llist_add(&cmd->tvc_completion_list, &vs->vs_completion_list);
+	vhost_work_queue(&vs->dev, &vs->vs_completion_work);
+}
+
 static u32 vhost_scsi_sess_get_index(struct se_session *se_sess)
 {
 	return 0;
@@ -366,28 +376,15 @@ static int vhost_scsi_get_cmd_state(struct se_cmd *se_cmd)
 	return 0;
 }
 
-static void vhost_scsi_complete_cmd(struct vhost_scsi_cmd *cmd)
-{
-	struct vhost_scsi *vs = cmd->tvc_vhost;
-
-	llist_add(&cmd->tvc_completion_list, &vs->vs_completion_list);
-
-	vhost_work_queue(&vs->dev, &vs->vs_completion_work);
-}
-
 static int vhost_scsi_queue_data_in(struct se_cmd *se_cmd)
 {
-	struct vhost_scsi_cmd *cmd = container_of(se_cmd,
-				struct vhost_scsi_cmd, tvc_se_cmd);
-	vhost_scsi_complete_cmd(cmd);
+	transport_generic_free_cmd(se_cmd, 0);
 	return 0;
 }
 
 static int vhost_scsi_queue_status(struct se_cmd *se_cmd)
 {
-	struct vhost_scsi_cmd *cmd = container_of(se_cmd,
-				struct vhost_scsi_cmd, tvc_se_cmd);
-	vhost_scsi_complete_cmd(cmd);
+	transport_generic_free_cmd(se_cmd, 0);
 	return 0;
 }
 
@@ -433,15 +430,6 @@ static void vhost_scsi_free_evt(struct vhost_scsi *vs, struct vhost_scsi_evt *ev
 	return evt;
 }
 
-static void vhost_scsi_free_cmd(struct vhost_scsi_cmd *cmd)
-{
-	struct se_cmd *se_cmd = &cmd->tvc_se_cmd;
-
-	/* TODO locking against target/backend threads? */
-	transport_generic_free_cmd(se_cmd, 0);
-
-}
-
 static int vhost_scsi_check_stop_free(struct se_cmd *se_cmd)
 {
 	return target_put_sess_cmd(se_cmd);
@@ -560,7 +548,7 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
 		} else
 			pr_err("Faulted on virtio_scsi_cmd_resp\n");
 
-		vhost_scsi_free_cmd(cmd);
+		vhost_scsi_release_cmd_res(se_cmd);
 	}
 
 	vq = -1;
@@ -1092,7 +1080,7 @@ static void vhost_scsi_submission_work(struct work_struct *work)
 						      &prot_iter, exp_data_len,
 						      &data_iter))) {
 				vq_err(vq, "Failed to map iov to sgl\n");
-				vhost_scsi_release_cmd(&cmd->tvc_se_cmd);
+				vhost_scsi_release_cmd_res(&cmd->tvc_se_cmd);
 				goto err;
 			}
 		}
-- 
1.8.3.1


  parent reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-21 18:23 [PATCH 0/8] vhost scsi: fixes and cleanups Mike Christie
2020-09-21 18:23 ` [PATCH 1/8] vhost vdpa: fix vhost_vdpa_open error handling Mike Christie
2020-09-22  1:58   ` Jason Wang
2020-09-21 18:23 ` [PATCH 2/8] vhost: add helper to check if a vq has been setup Mike Christie
2020-09-22  2:02   ` Jason Wang
2020-09-23 19:12     ` Mike Christie
2020-09-24  7:22       ` Jason Wang
2020-09-22  2:45   ` Bart Van Assche
2020-09-22 15:34     ` Michael Christie
2020-09-21 18:23 ` [PATCH 3/8] vhost scsi: alloc cmds per vq instead of session Mike Christie
2020-09-22  1:32   ` kernel test robot
2020-09-23  7:53   ` Dan Carpenter
2020-09-24  6:22   ` Michael S. Tsirkin
2020-09-24 15:31     ` Michael Christie
2020-09-21 18:23 ` Mike Christie [this message]
2020-09-22  2:48   ` [PATCH 4/8] vhost scsi: fix cmd completion race Bart Van Assche
2020-09-22  2:51     ` Bart Van Assche
2020-09-21 18:23 ` [PATCH 5/8] vhost scsi: add lun parser helper Mike Christie
2020-09-23 10:23   ` Paolo Bonzini
2020-09-21 18:23 ` [PATCH 6/8] vhost scsi: Add support for LUN resets Mike Christie
2020-09-21 18:23 ` [PATCH 7/8] vhost: remove work arg from vhost_work_flush Mike Christie
2020-09-22  2:01   ` Jason Wang
2020-09-21 18:23 ` [PATCH 8/8] vhost scsi: remove extra flushes Mike Christie

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