IB/srp: Implement SRP_CRED_REQ and SRP_AER_REQ

This patch adds support for SRP_CRED_REQ to avoid a lockup by targets
that use that mechanism to return credits to the initiator. This
prevents a lockup observed in the field where we would never add the
credits from the SRP_CRED_REQ to our current count, and would therefore
never send another command to the target.

Minimal support for SRP_AER_REQ is also added, as these messages can
also be used to convey additional credits to the initiator.

Based upon extensive debugging and code by Bart Van Assche and a bug
report by Chris Worley.

Signed-off-by: David Dillow <dillowda@ornl.gov>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

2 files changed, 103 insertions, 10 deletions

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index b8b09a4f012a..a54eee9324b6 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -83,6 +83,10 @@ static void srp_remove_one(struct ib_device *device);
 static void srp_recv_completion(struct ib_cq *cq, void *target_ptr);
 static void srp_send_completion(struct ib_cq *cq, void *target_ptr);
 static int srp_cm_handler(struct ib_cm_id *cm_id, struct ib_cm_event *event);
+static struct srp_iu *__srp_get_tx_iu(struct srp_target_port *target,
+                                      enum srp_iu_type iu_type);
+static int __srp_post_send(struct srp_target_port *target,
+                           struct srp_iu *iu, int len);
 
 static struct scsi_transport_template *ib_srp_transport_template;
 
@@ -896,6 +900,71 @@ static void srp_process_rsp(struct srp_target_port *target, struct srp_rsp *rsp)
         spin_unlock_irqrestore(target->scsi_host->host_lock, flags);
 }
 
+static int srp_response_common(struct srp_target_port *target, s32 req_delta,
+                               void *rsp, int len)
+{
+        struct ib_device *dev;
+        unsigned long flags;
+        struct srp_iu *iu;
+        int err = 1;
+
+        dev = target->srp_host->srp_dev->dev;
+
+        spin_lock_irqsave(target->scsi_host->host_lock, flags);
+        target->req_lim += req_delta;
+
+        iu = __srp_get_tx_iu(target, SRP_IU_RSP);
+        if (!iu) {
+                shost_printk(KERN_ERR, target->scsi_host, PFX
+                             "no IU available to send response\n");
+                goto out;
+        }
+
+        ib_dma_sync_single_for_cpu(dev, iu->dma, len, DMA_TO_DEVICE);
+        memcpy(iu->buf, rsp, len);
+        ib_dma_sync_single_for_device(dev, iu->dma, len, DMA_TO_DEVICE);
+
+        err = __srp_post_send(target, iu, len);
+        if (err)
+                shost_printk(KERN_ERR, target->scsi_host, PFX
+                             "unable to post response: %d\n", err);
+
+out:
+        spin_unlock_irqrestore(target->scsi_host->host_lock, flags);
+        return err;
+}
+
+static void srp_process_cred_req(struct srp_target_port *target,
+                                 struct srp_cred_req *req)
+{
+        struct srp_cred_rsp rsp = {
+                .opcode = SRP_CRED_RSP,
+                .tag = req->tag,
+        };
+        s32 delta = be32_to_cpu(req->req_lim_delta);
+
+        if (srp_response_common(target, delta, &rsp, sizeof rsp))
+                shost_printk(KERN_ERR, target->scsi_host, PFX
+                             "problems processing SRP_CRED_REQ\n");
+}
+
+static void srp_process_aer_req(struct srp_target_port *target,
+                                struct srp_aer_req *req)
+{
+        struct srp_aer_rsp rsp = {
+                .opcode = SRP_AER_RSP,
+                .tag = req->tag,
+        };
+        s32 delta = be32_to_cpu(req->req_lim_delta);
+
+        shost_printk(KERN_ERR, target->scsi_host, PFX
+                     "ignoring AER for LUN %llu\n", be64_to_cpu(req->lun));
+
+        if (srp_response_common(target, delta, &rsp, sizeof rsp))
+                shost_printk(KERN_ERR, target->scsi_host, PFX
+                             "problems processing SRP_AER_REQ\n");
+}
+
 static void srp_handle_recv(struct srp_target_port *target, struct ib_wc *wc)
 {
         struct ib_device *dev;
@@ -923,6 +992,14 @@ static void srp_handle_recv(struct srp_target_port *target, struct ib_wc *wc)
                 srp_process_rsp(target, iu->buf);
                 break;
 
+        case SRP_CRED_REQ:
+                srp_process_cred_req(target, iu->buf);
+                break;
+
+        case SRP_AER_REQ:
+                srp_process_aer_req(target, iu->buf);
+                break;
+
         case SRP_T_LOGOUT:
                 /* XXX Handle target logout */
                 shost_printk(KERN_WARNING, target->scsi_host,
@@ -985,23 +1062,36 @@ static void srp_send_completion(struct ib_cq *cq, void *target_ptr)
  * Must be called with target->scsi_host->host_lock held to protect
  * req_lim and tx_head.  Lock cannot be dropped between call here and
  * call to __srp_post_send().
+ *
+ * Note:
+ * An upper limit for the number of allocated information units for each
+ * request type is:
+ * - SRP_IU_CMD: SRP_CMD_SQ_SIZE, since the SCSI mid-layer never queues
+ *   more than Scsi_Host.can_queue requests.
+ * - SRP_IU_TSK_MGMT: SRP_TSK_MGMT_SQ_SIZE.
+ * - SRP_IU_RSP: 1, since a conforming SRP target never sends more than
+ *   one unanswered SRP request to an initiator.
  */
 static struct srp_iu *__srp_get_tx_iu(struct srp_target_port *target,
-                                        enum srp_request_type req_type)
+                                      enum srp_iu_type iu_type)
 {
-        s32 rsv = (req_type == SRP_REQ_TASK_MGMT) ? 0 : SRP_TSK_MGMT_SQ_SIZE;
+        s32 rsv = (iu_type == SRP_IU_TSK_MGMT) ? 0 : SRP_TSK_MGMT_SQ_SIZE;
+        struct srp_iu *iu;
 
         srp_send_completion(target->send_cq, target);
 
         if (target->tx_head - target->tx_tail >= SRP_SQ_SIZE)
                 return NULL;
 
-        if (target->req_lim <= rsv) {
+        /* Initiator responses to target requests do not consume credits */
+        if (target->req_lim <= rsv && iu_type != SRP_IU_RSP) {
                 ++target->zero_req_lim;
                 return NULL;
         }
 
-        return target->tx_ring[target->tx_head & SRP_SQ_MASK];
+        iu = target->tx_ring[target->tx_head & SRP_SQ_MASK];
+        iu->type = iu_type;
+        return iu;
 }
 
 /*
@@ -1030,7 +1120,8 @@ static int __srp_post_send(struct srp_target_port *target,
 
         if (!ret) {
                 ++target->tx_head;
-                --target->req_lim;
+                if (iu->type != SRP_IU_RSP)
+                        --target->req_lim;
         }
 
         return ret;
@@ -1056,7 +1147,7 @@ static int srp_queuecommand(struct scsi_cmnd *scmnd,
                 return 0;
         }
 
-        iu = __srp_get_tx_iu(target, SRP_REQ_NORMAL);
+        iu = __srp_get_tx_iu(target, SRP_IU_CMD);
         if (!iu)
                 goto err;
 
@@ -1363,7 +1454,7 @@ static int srp_send_tsk_mgmt(struct srp_target_port *target,
 
         init_completion(&req->done);
 
-        iu = __srp_get_tx_iu(target, SRP_REQ_TASK_MGMT);
+        iu = __srp_get_tx_iu(target, SRP_IU_TSK_MGMT);
         if (!iu)
                 goto out;
 
diff --git a/drivers/infiniband/ulp/srp/ib_srp.h b/drivers/infiniband/ulp/srp/ib_srp.h
index 7a959d5f2fa6..ed0dce9e479f 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.h
+++ b/drivers/infiniband/ulp/srp/ib_srp.h
@@ -82,9 +82,10 @@ enum srp_target_state {
         SRP_TARGET_REMOVED
 };
 
-enum srp_request_type {
-        SRP_REQ_NORMAL,
-        SRP_REQ_TASK_MGMT,
+enum srp_iu_type {
+        SRP_IU_CMD,
+        SRP_IU_TSK_MGMT,
+        SRP_IU_RSP,
 };
 
 struct srp_device {
@@ -171,6 +172,7 @@ struct srp_iu {
         void                   *buf;
         size_t                  size;
         enum dma_data_direction direction;
+        enum srp_iu_type        type;
 };
 
 #endif /* IB_SRP_H */