[PATCH 6/9] scsi: iscsi: Remove unneeded task state check

From: Mike Christie <michael.christie@oracle.com>
To: lduncan@suse.com, cleech@redhat.com, martin.petersen@oracle.com,
	linux-scsi@vger.kernel.org, jejb@linux.ibm.com
Cc: Mike Christie <michael.christie@oracle.com>, Wu Bo <wubo40@huawei.com>
Subject: [PATCH 6/9] scsi: iscsi: Remove unneeded task state check
Date: Thu, 16 Jun 2022 17:45:54 -0500	[thread overview]
Message-ID: <20220616224557.115234-7-michael.christie@oracle.com> (raw)
In-Reply-To: <20220616224557.115234-1-michael.christie@oracle.com>

Commit 5923d64b7ab6 ("scsi: libiscsi: Drop taskqueuelock") added an extra
task->state because for commit 6f8830f5bbab ("scsi: libiscsi: add lock
around task lists to fix list corruption regression") we didn't know why we
ended up with cmds on the list and thought it might have been a bad target
sending a response while we were still sending the cmd. We were never able
to get a target to send us a response early, because it turns out the bug
was just a race in libiscsi/libiscsi_tcp where:

 1. iscsi_tcp_r2t_rsp() queues a r2t to tcp_task->r2tqueue.

 2. iscsi_tcp_task_xmit() runs iscsi_tcp_get_curr_r2t() and sees we have a
    r2t. It dequeues it and iscsi_tcp_task_xmit() starts to process it.

 3. iscsi_tcp_r2t_rsp() runs iscsi_requeue_task() and puts the task on the
    requeue list.

 4. iscsi_tcp_task_xmit() sends the data for r2t. This is the final chunk
    of data, so the cmd is done.

 5. target sends the response.

 6. On a different CPU from #3, iscsi_complete_task() processes the
    response.  Since there was no common lock for the list, the lists/tasks
    pointers are not fully in sync, so could end up with list corruption.

Since it was just a race on our side, remove the extra check and fix up the
comments.

Reviewed-by: Wu Bo <wubo40@huawei.com>
Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
---
 drivers/scsi/libiscsi.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
index 44283014c4eb..1d646f02d516 100644
--- a/drivers/scsi/libiscsi.c
+++ b/drivers/scsi/libiscsi.c
@@ -567,16 +567,19 @@ static bool cleanup_queued_task(struct iscsi_task *task)
 	struct iscsi_conn *conn = task->conn;
 	bool early_complete = false;
 
-	/* Bad target might have completed task while it was still running */
+	/*
+	 * We might have raced where we handled a R2T early and got a response
+	 * but have not yet taken the task off the requeue list, then a TMF or
+	 * recovery happened and so we can still see it here.
+	 */
 	if (task->state == ISCSI_TASK_COMPLETED)
 		early_complete = true;
 
 	if (!list_empty(&task->running)) {
 		list_del_init(&task->running);
 		/*
-		 * If it's on a list but still running, this could be from
-		 * a bad target sending a rsp early, cleanup from a TMF, or
-		 * session recovery.
+		 * If it's on a list but still running this could be cleanup
+		 * from a TMF or session recovery.
 		 */
 		if (task->state == ISCSI_TASK_RUNNING ||
 		    task->state == ISCSI_TASK_COMPLETED)
@@ -1485,7 +1488,7 @@ static int iscsi_xmit_task(struct iscsi_conn *conn, struct iscsi_task *task,
 	}
 	/* regular RX path uses back_lock */
 	spin_lock(&conn->session->back_lock);
-	if (rc && task->state == ISCSI_TASK_RUNNING) {
+	if (rc) {
 		/*
 		 * get an extra ref that is released next time we access it
 		 * as conn->task above.
-- 
2.25.1

