IB/core: Use qp->usecnt to track multicast attach/detach

Just as we don't allow PDs, CQs, etc. to be destroyed if there are QPs
that are attached to them, don't let a QP be destroyed if there are
multicast group(s) attached to it.  Use the existing usecnt field of
struct ib_qp which was added by commit 0e0ec7e ("RDMA/core: Export
ib_open_qp() to share XRC TGT QPs") to track this.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

2 files changed, 13 insertions, 3 deletions

diff --git a/drivers/infiniband/core/verbs.c b/drivers/infiniband/core/verbs.c
index 575b78045aaf..c5b94d647e1e 100644
--- a/drivers/infiniband/core/verbs.c
+++ b/drivers/infiniband/core/verbs.c
@@ -1183,23 +1183,33 @@ EXPORT_SYMBOL(ib_dealloc_fmr);
 
 int ib_attach_mcast(struct ib_qp *qp, union ib_gid *gid, u16 lid)
 {
+        int ret;
+
         if (!qp->device->attach_mcast)
                 return -ENOSYS;
         if (gid->raw[0] != 0xff || qp->qp_type != IB_QPT_UD)
                 return -EINVAL;
 
-        return qp->device->attach_mcast(qp, gid, lid);
+        ret = qp->device->attach_mcast(qp, gid, lid);
+        if (!ret)
+                atomic_inc(&qp->usecnt);
+        return ret;
 }
 EXPORT_SYMBOL(ib_attach_mcast);
 
 int ib_detach_mcast(struct ib_qp *qp, union ib_gid *gid, u16 lid)
 {
+        int ret;
+
         if (!qp->device->detach_mcast)
                 return -ENOSYS;
         if (gid->raw[0] != 0xff || qp->qp_type != IB_QPT_UD)
                 return -EINVAL;
 
-        return qp->device->detach_mcast(qp, gid, lid);
+        ret = qp->device->detach_mcast(qp, gid, lid);
+        if (!ret)
+                atomic_dec(&qp->usecnt);
+        return ret;
 }
 EXPORT_SYMBOL(ib_detach_mcast);
 
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index c3cca5a4dacd..c84d1016618e 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -964,7 +964,7 @@ struct ib_qp {
         struct ib_srq          *srq;
         struct ib_xrcd         *xrcd; /* XRC TGT QPs only */
         struct list_head        xrcd_list;
-        atomic_t                usecnt; /* count times opened */
+        atomic_t                usecnt; /* count times opened, mcast attaches */
         struct list_head        open_list;
         struct ib_qp           *real_qp;
         struct ib_uobject      *uobject;