IB/srp: Fix a race condition

Avoid a crash caused by the scmnd->scsi_done(scmnd) call in
srp_process_rsp() being invoked with scsi_done == NULL.  This can
happen if a reply is received during or after a command abort.

Reported-by: Joseph Glanville <joseph.glanville@orionvm.com.au>
Reference: http://marc.info/?l=linux-rdma&m=134314367801595
Cc: <stable@vger.kernel.org>
Acked-by: David Dillow <dillowda@ornl.gov>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index bcbf22e..1b5b0c7 100644 (file)
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -586,24 +586,62 @@ static void srp_unmap_data(struct scsi_cmnd *scmnd,
                        scmnd->sc_data_direction);
 }
 
-static void srp_remove_req(struct srp_target_port *target,
-                          struct srp_request *req, s32 req_lim_delta)
+/**
+ * srp_claim_req - Take ownership of the scmnd associated with a request.
+ * @target: SRP target port.
+ * @req: SRP request.
+ * @scmnd: If NULL, take ownership of @req->scmnd. If not NULL, only take
+ *         ownership of @req->scmnd if it equals @scmnd.
+ *
+ * Return value:
+ * Either NULL or a pointer to the SCSI command the caller became owner of.
+ */
+static struct scsi_cmnd *srp_claim_req(struct srp_target_port *target,
+                                      struct srp_request *req,
+                                      struct scsi_cmnd *scmnd)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&target->lock, flags);
+       if (!scmnd) {
+               scmnd = req->scmnd;
+               req->scmnd = NULL;
+       } else if (req->scmnd == scmnd) {
+               req->scmnd = NULL;
+       } else {
+               scmnd = NULL;
+       }
+       spin_unlock_irqrestore(&target->lock, flags);
+
+       return scmnd;
+}
+
+/**
+ * srp_free_req() - Unmap data and add request to the free request list.
+ */
+static void srp_free_req(struct srp_target_port *target,
+                        struct srp_request *req, struct scsi_cmnd *scmnd,
+                        s32 req_lim_delta)
 {
        unsigned long flags;
 
-       srp_unmap_data(req->scmnd, target, req);
+       srp_unmap_data(scmnd, target, req);
+
        spin_lock_irqsave(&target->lock, flags);
        target->req_lim += req_lim_delta;
-       req->scmnd = NULL;
        list_add_tail(&req->list, &target->free_reqs);
        spin_unlock_irqrestore(&target->lock, flags);
 }
 
 static void srp_reset_req(struct srp_target_port *target, struct srp_request *req)
 {
-       req->scmnd->result = DID_RESET << 16;
-       req->scmnd->scsi_done(req->scmnd);
-       srp_remove_req(target, req, 0);
+       struct scsi_cmnd *scmnd = srp_claim_req(target, req, NULL);
+
+       if (scmnd) {
+               scmnd->result = DID_RESET << 16;
+               scmnd->scsi_done(scmnd);
+               srp_free_req(target, req, scmnd, 0);
+       }
 }
 
 static int srp_reconnect_target(struct srp_target_port *target)
@@ -1073,11 +1111,18 @@ 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 = req->scmnd;
-               if (!scmnd)
+               scmnd = srp_claim_req(target, req, NULL);
+               if (!scmnd) {
                        shost_printk(KERN_ERR, target->scsi_host,
                                     "Null scmnd for RSP w/tag %016llx\n",
                                     (unsigned long long) rsp->tag);
+
+                       spin_lock_irqsave(&target->lock, flags);
+                       target->req_lim += be32_to_cpu(rsp->req_lim_delta);
+                       spin_unlock_irqrestore(&target->lock, flags);
+
+                       return;
+               }
                scmnd->result = rsp->status;
 
                if (rsp->flags & SRP_RSP_FLAG_SNSVALID) {
@@ -1092,7 +1137,9 @@ static void srp_process_rsp(struct srp_target_port *target, struct srp_rsp *rsp)
                else if (rsp->flags & (SRP_RSP_FLAG_DIOVER | SRP_RSP_FLAG_DIUNDER))
                        scsi_set_resid(scmnd, be32_to_cpu(rsp->data_in_res_cnt));
 
-               srp_remove_req(target, req, be32_to_cpu(rsp->req_lim_delta));
+               srp_free_req(target, req, scmnd,
+                            be32_to_cpu(rsp->req_lim_delta));
+
                scmnd->host_scribble = NULL;
                scmnd->scsi_done(scmnd);
        }
@@ -1631,25 +1678,17 @@ static int srp_abort(struct scsi_cmnd *scmnd)
 {
        struct srp_target_port *target = host_to_target(scmnd->device->host);
        struct srp_request *req = (struct srp_request *) scmnd->host_scribble;
-       int ret = SUCCESS;
 
        shost_printk(KERN_ERR, target->scsi_host, "SRP abort called\n");
 
-       if (!req || target->qp_in_error)
+       if (!req || target->qp_in_error || !srp_claim_req(target, req, scmnd))
                return FAILED;
-       if (srp_send_tsk_mgmt(target, req->index, scmnd->device->lun,
-                             SRP_TSK_ABORT_TASK))
-               return FAILED;
-
-       if (req->scmnd) {
-               if (!target->tsk_mgmt_status) {
-                       srp_remove_req(target, req, 0);
-                       scmnd->result = DID_ABORT << 16;
-               } else
-                       ret = FAILED;
-       }
+       srp_send_tsk_mgmt(target, req->index, scmnd->device->lun,
+                         SRP_TSK_ABORT_TASK);
+       srp_free_req(target, req, scmnd, 0);
+       scmnd->result = DID_ABORT << 16;
 
-       return ret;
+       return SUCCESS;
 }
 
 static int srp_reset_device(struct scsi_cmnd *scmnd)