[PATCH v3 7/7] IB/srp: Fix a race condition between failing I/O and I/O completion

[Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>]

Avoid that srp_terminate_io() can access req->scmnd after it has been
cleared by the I/O completion code. Do this by protecting req->scmnd
accesses from srp_terminate_io() via locking

Signed-off-by: Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>
Acked-by: Sagi Grimberg <sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Cc: Sebastian Riemer <sebastian.riemer-EIkl63zCoXaH+58JC4qpiA@public.gmane.org>
Cc: Roland Dreier <roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 drivers/infiniband/ulp/srp/ib_srp.c | 33 ++++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index a64e469..66a908b 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -783,6 +783,7 @@ static void srp_unmap_data(struct scsi_cmnd *scmnd,
  * srp_claim_req - Take ownership of the scmnd associated with a request.
  * @target: SRP target port.
  * @req: SRP request.
+ * @sdev: If not NULL, only take ownership for this SCSI device.
  * @scmnd: If NULL, take ownership of @req->scmnd. If not NULL, only take
  *         ownership of @req->scmnd if it equals @scmnd.
  *
@@ -791,16 +792,17 @@ static void srp_unmap_data(struct scsi_cmnd *scmnd,
  */
 static struct scsi_cmnd *srp_claim_req(struct srp_target_port *target,
 				       struct srp_request *req,
+				       struct scsi_device *sdev,
 				       struct scsi_cmnd *scmnd)
 {
 	unsigned long flags;
 
 	spin_lock_irqsave(&target->lock, flags);
-	if (!scmnd) {
+	if (req->scmnd &&
+	    (!sdev || req->scmnd->device == sdev) &&
+	    (!scmnd || req->scmnd == scmnd)) {
 		scmnd = req->scmnd;
 		req->scmnd = NULL;
-	} else if (req->scmnd == scmnd) {
-		req->scmnd = NULL;
 	} else {
 		scmnd = NULL;
 	}
@@ -827,9 +829,10 @@ static void srp_free_req(struct srp_target_port *target,
 }
 
 static void srp_finish_req(struct srp_target_port *target,
-			   struct srp_request *req, int result)
+			   struct srp_request *req, struct scsi_device *sdev,
+			   int result)
 {
-	struct scsi_cmnd *scmnd = srp_claim_req(target, req, NULL);
+	struct scsi_cmnd *scmnd = srp_claim_req(target, req, sdev, NULL);
 
 	if (scmnd) {
 		srp_free_req(target, req, scmnd, 0);
@@ -841,11 +844,20 @@ static void srp_finish_req(struct srp_target_port *target,
 static void srp_terminate_io(struct srp_rport *rport)
 {
 	struct srp_target_port *target = rport->lld_data;
+	struct Scsi_Host *shost = target->scsi_host;
+	struct scsi_device *sdev;
 	int i;
 
+	/*
+	 * Invoking srp_terminate_io() while srp_queuecommand() is running
+	 * is not safe. Hence the warning statement below.
+	 */
+	shost_for_each_device(sdev, shost)
+		WARN_ON_ONCE(sdev->request_queue->request_fn_active);
+
 	for (i = 0; i < target->req_ring_size; ++i) {
 		struct srp_request *req = &target->req_ring[i];
-		srp_finish_req(target, req, DID_TRANSPORT_FAILFAST << 16);
+		srp_finish_req(target, req, NULL, DID_TRANSPORT_FAILFAST << 16);
 	}
 }
 
@@ -882,7 +894,7 @@ static int srp_rport_reconnect(struct srp_rport *rport)
 
 	for (i = 0; i < target->req_ring_size; ++i) {
 		struct srp_request *req = &target->req_ring[i];
-		srp_finish_req(target, req, DID_RESET << 16);
+		srp_finish_req(target, req, NULL, DID_RESET << 16);
 	}
 
 	INIT_LIST_HEAD(&target->free_tx);
@@ -1290,7 +1302,7 @@ static void srp_process_rsp(struct srp_target_port *target, struct srp_rsp *rsp)
 		complete(&target->tsk_mgmt_done);
 	} else {
 		req = &target->req_ring[rsp->tag];
-		scmnd = srp_claim_req(target, req, NULL);
+		scmnd = srp_claim_req(target, req, NULL, NULL);
 		if (!scmnd) {
 			shost_printk(KERN_ERR, target->scsi_host,
 				     "Null scmnd for RSP w/tag %016llx\n",
@@ -2008,7 +2020,7 @@ static int srp_abort(struct scsi_cmnd *scmnd)
 
 	shost_printk(KERN_ERR, target->scsi_host, "SRP abort called\n");
 
-	if (!req || !srp_claim_req(target, req, scmnd))
+	if (!req || !srp_claim_req(target, req, NULL, scmnd))
 		return SUCCESS;
 	if (srp_send_tsk_mgmt(target, req->index, scmnd->device->lun,
 			      SRP_TSK_ABORT_TASK) == 0)
@@ -2039,8 +2051,7 @@ static int srp_reset_device(struct scsi_cmnd *scmnd)
 
 	for (i = 0; i < target->req_ring_size; ++i) {
 		struct srp_request *req = &target->req_ring[i];
-		if (req->scmnd && req->scmnd->device == scmnd->device)
-			srp_finish_req(target, req, DID_RESET << 16);
+		srp_finish_req(target, req, scmnd->device, DID_RESET << 16);
 	}
 
 	return SUCCESS;
-- 
1.8.4.5

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