nvme_fcloop: refactor host/target io job access

The split between what the host accesses on its flows vs what the
target side accesses was flawed. Abort handling didn't properly
clear initiator vs target structure cross-reference and locks
weren't used for synchronization. Thus, there were issues of
freeing structures too soon and access after free.

A couple of these existed pre the IN_ISR mods, but when the
target upcalls were converted to work items, thus adding delays
between the 2 sides of accesses, the problems became pronounced.

Resolve by:
- tracking io state mainly in the tgt-side io structure.
- make the tgt-side io structure released by reference not by
  code flow.
- when changing initiator structures, use locks for
  synchronization
- aborts are clearly tracked for which side saw the abort, and
  after seeing the abort, cross-references are cleared under lock.

Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/fcloop.c

@@ -242,13 +242,22 @@ struct fcloop_lsreq {
 	int				status;
 };
 
+enum {
+	INI_IO_START		= 0,
+	INI_IO_ACTIVE		= 1,
+	INI_IO_ABORTED		= 2,
+	INI_IO_COMPLETED	= 3,
+};
+
 struct fcloop_fcpreq {
 	struct fcloop_tport		*tport;
 	struct nvmefc_fcp_req		*fcpreq;
 	spinlock_t			reqlock;
 	u16				status;
+	u32				inistate;
 	bool				active;
 	bool				aborted;
+	struct kref			ref;
 	struct work_struct		fcp_rcv_work;
 	struct work_struct		abort_rcv_work;
 	struct work_struct		tio_done_work;
@@ -258,6 +267,7 @@ struct fcloop_fcpreq {
 struct fcloop_ini_fcpreq {
 	struct nvmefc_fcp_req		*fcpreq;
 	struct fcloop_fcpreq		*tfcp_req;
+	spinlock_t			inilock;
 };
 
 static inline struct fcloop_lsreq *
@@ -349,24 +359,24 @@ fcloop_xmt_ls_rsp(struct nvmet_fc_target_port *tport,
 }
 
 static void
-fcloop_fcp_recv_work(struct work_struct *work)
+fcloop_tfcp_req_free(struct kref *ref)
 {
 	struct fcloop_fcpreq *tfcp_req =
-		container_of(work, struct fcloop_fcpreq, fcp_rcv_work);
-	struct nvmefc_fcp_req *fcpreq = tfcp_req->fcpreq;
-	struct fcloop_ini_fcpreq *inireq = NULL;
-	int ret = 0;
+		container_of(ref, struct fcloop_fcpreq, ref);
 
-	ret = nvmet_fc_rcv_fcp_req(tfcp_req->tport->targetport,
-				&tfcp_req->tgt_fcp_req,
-				fcpreq->cmdaddr, fcpreq->cmdlen);
-	if (ret) {
-		inireq = fcpreq->private;
-		inireq->tfcp_req = NULL;
+	kfree(tfcp_req);
+}
 
-		fcpreq->status = tfcp_req->status;
-		fcpreq->done(fcpreq);
-	}
+static void
+fcloop_tfcp_req_put(struct fcloop_fcpreq *tfcp_req)
+{
+	kref_put(&tfcp_req->ref, fcloop_tfcp_req_free);
+}
+
+static int
+fcloop_tfcp_req_get(struct fcloop_fcpreq *tfcp_req)
+{
+	return kref_get_unless_zero(&tfcp_req->ref);
 }
 
 static void
@@ -377,11 +387,52 @@ fcloop_call_host_done(struct nvmefc_fcp_req *fcpreq,
 
 	if (fcpreq) {
 		inireq = fcpreq->private;
+		spin_lock(&inireq->inilock);
 		inireq->tfcp_req = NULL;
+		spin_unlock(&inireq->inilock);
 
 		fcpreq->status = status;
 		fcpreq->done(fcpreq);
 	}
+
+	/* release original io reference on tgt struct */
+	fcloop_tfcp_req_put(tfcp_req);
+}
+
+static void
+fcloop_fcp_recv_work(struct work_struct *work)
+{
+	struct fcloop_fcpreq *tfcp_req =
+		container_of(work, struct fcloop_fcpreq, fcp_rcv_work);
+	struct nvmefc_fcp_req *fcpreq = tfcp_req->fcpreq;
+	int ret = 0;
+	bool aborted = false;
+
+	spin_lock(&tfcp_req->reqlock);
+	switch (tfcp_req->inistate) {
+	case INI_IO_START:
+		tfcp_req->inistate = INI_IO_ACTIVE;
+		break;
+	case INI_IO_ABORTED:
+		aborted = true;
+		break;
+	default:
+		spin_unlock(&tfcp_req->reqlock);
+		WARN_ON(1);
+		return;
+	}
+	spin_unlock(&tfcp_req->reqlock);
+
+	if (unlikely(aborted))
+		ret = -ECANCELED;
+	else
+		ret = nvmet_fc_rcv_fcp_req(tfcp_req->tport->targetport,
+				&tfcp_req->tgt_fcp_req,
+				fcpreq->cmdaddr, fcpreq->cmdlen);
+	if (ret)
+		fcloop_call_host_done(fcpreq, tfcp_req, ret);
+
+	return;
 }
 
 static void
@@ -389,7 +440,29 @@ fcloop_fcp_abort_recv_work(struct work_struct *work)
 {
 	struct fcloop_fcpreq *tfcp_req =
 		container_of(work, struct fcloop_fcpreq, abort_rcv_work);
-	struct nvmefc_fcp_req *fcpreq = tfcp_req->fcpreq;
+	struct nvmefc_fcp_req *fcpreq;
+	bool completed = false;
+
+	spin_lock(&tfcp_req->reqlock);
+	fcpreq = tfcp_req->fcpreq;
+	switch (tfcp_req->inistate) {
+	case INI_IO_ABORTED:
+		break;
+	case INI_IO_COMPLETED:
+		completed = true;
+		break;
+	default:
+		spin_unlock(&tfcp_req->reqlock);
+		WARN_ON(1);
+		return;
+	}
+	spin_unlock(&tfcp_req->reqlock);
+
+	if (unlikely(completed)) {
+		/* remove reference taken in original abort downcall */
+		fcloop_tfcp_req_put(tfcp_req);
+		return;
+	}
 
 	if (tfcp_req->tport->targetport)
 		nvmet_fc_rcv_fcp_abort(tfcp_req->tport->targetport,
@@ -400,6 +473,7 @@ fcloop_fcp_abort_recv_work(struct work_struct *work)
 	spin_unlock(&tfcp_req->reqlock);
 
 	fcloop_call_host_done(fcpreq, tfcp_req, -ECANCELED);
+	/* call_host_done releases reference for abort downcall */
 }
 
 /*
@@ -415,12 +489,10 @@ fcloop_tgt_fcprqst_done_work(struct work_struct *work)
 
 	spin_lock(&tfcp_req->reqlock);
 	fcpreq = tfcp_req->fcpreq;
-	tfcp_req->fcpreq = NULL;
+	tfcp_req->inistate = INI_IO_COMPLETED;
 	spin_unlock(&tfcp_req->reqlock);
 
 	fcloop_call_host_done(fcpreq, tfcp_req, tfcp_req->status);
-
-	kfree(tfcp_req);
 }
 
 
@@ -443,12 +515,16 @@ fcloop_fcp_req(struct nvme_fc_local_port *localport,
 
 	inireq->fcpreq = fcpreq;
 	inireq->tfcp_req = tfcp_req;
+	spin_lock_init(&inireq->inilock);
+
 	tfcp_req->fcpreq = fcpreq;
 	tfcp_req->tport = rport->targetport->private;
+	tfcp_req->inistate = INI_IO_START;
 	spin_lock_init(&tfcp_req->reqlock);
 	INIT_WORK(&tfcp_req->fcp_rcv_work, fcloop_fcp_recv_work);
 	INIT_WORK(&tfcp_req->abort_rcv_work, fcloop_fcp_abort_recv_work);
 	INIT_WORK(&tfcp_req->tio_done_work, fcloop_tgt_fcprqst_done_work);
+	kref_init(&tfcp_req->ref);
 
 	schedule_work(&tfcp_req->fcp_rcv_work);
 
@@ -648,7 +724,14 @@ fcloop_fcp_abort(struct nvme_fc_local_port *localport,
 			struct nvmefc_fcp_req *fcpreq)
 {
 	struct fcloop_ini_fcpreq *inireq = fcpreq->private;
-	struct fcloop_fcpreq *tfcp_req = inireq->tfcp_req;
+	struct fcloop_fcpreq *tfcp_req;
+	bool abortio = true;
+
+	spin_lock(&inireq->inilock);
+	tfcp_req = inireq->tfcp_req;
+	if (tfcp_req)
+		fcloop_tfcp_req_get(tfcp_req);
+	spin_unlock(&inireq->inilock);
 
 	if (!tfcp_req)
 		/* abort has already been called */
@@ -656,11 +739,31 @@ fcloop_fcp_abort(struct nvme_fc_local_port *localport,
 
 	/* break initiator/target relationship for io */
 	spin_lock(&tfcp_req->reqlock);
-	inireq->tfcp_req = NULL;
-	tfcp_req->fcpreq = NULL;
+	switch (tfcp_req->inistate) {
+	case INI_IO_START:
+	case INI_IO_ACTIVE:
+		tfcp_req->inistate = INI_IO_ABORTED;
+		break;
+	case INI_IO_COMPLETED:
+		abortio = false;
+		break;
+	default:
+		spin_unlock(&tfcp_req->reqlock);
+		WARN_ON(1);
+		return;
+	}
 	spin_unlock(&tfcp_req->reqlock);
 
-	WARN_ON(!schedule_work(&tfcp_req->abort_rcv_work));
+	if (abortio)
+		/* leave the reference while the work item is scheduled */
+		WARN_ON(!schedule_work(&tfcp_req->abort_rcv_work));
+	else  {
+		/*
+		 * as the io has already had the done callback made,
+		 * nothing more to do. So release the reference taken above
+		 */
+		fcloop_tfcp_req_put(tfcp_req);
+	}
 }
 
 static void