RDMA/cxgb4: Serialize calls to CQ's comp_handler

Commit 01e7da6ba53c ("RDMA/cxgb4: Make sure flush CQ entries are
collected on connection close") introduced a potential problem where a
CQ's comp_handler can get called simultaneously from different places
in the iw_cxgb4 driver.  This does not comply with
Documentation/infiniband/core_locking.txt, which states that at a
given point of time, there should be only one callback per CQ should
be active.

This problem was reported by Parav Pandit <Parav.Pandit@Emulex.Com>.
Based on discussion between Parav Pandit and Steve Wise, this patch
fixes the above problem by serializing the calls to a CQ's
comp_handler using a spin_lock.

Reported-by: Parav Pandit <Parav.Pandit@Emulex.Com>
Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/infiniband/hw/cxgb4/ev.c b/drivers/infiniband/hw/cxgb4/ev.c
index c13041a0aeba..397cb36cf103 100644
--- a/drivers/infiniband/hw/cxgb4/ev.c
+++ b/drivers/infiniband/hw/cxgb4/ev.c
@@ -42,6 +42,7 @@ static void post_qp_event(struct c4iw_dev *dev, struct c4iw_cq *chp,
 {
         struct ib_event event;
         struct c4iw_qp_attributes attrs;
+        unsigned long flag;
 
         if ((qhp->attr.state == C4IW_QP_STATE_ERROR) ||
             (qhp->attr.state == C4IW_QP_STATE_TERMINATE)) {
@@ -72,7 +73,9 @@ static void post_qp_event(struct c4iw_dev *dev, struct c4iw_cq *chp,
         if (qhp->ibqp.event_handler)
                 (*qhp->ibqp.event_handler)(&event, qhp->ibqp.qp_context);
 
+        spin_lock_irqsave(&chp->comp_handler_lock, flag);
         (*chp->ibcq.comp_handler)(&chp->ibcq, chp->ibcq.cq_context);
+        spin_unlock_irqrestore(&chp->comp_handler_lock, flag);
 }
 
 void c4iw_ev_dispatch(struct c4iw_dev *dev, struct t4_cqe *err_cqe)
@@ -183,11 +186,14 @@ out:
 int c4iw_ev_handler(struct c4iw_dev *dev, u32 qid)
 {
         struct c4iw_cq *chp;
+        unsigned long flag;
 
         chp = get_chp(dev, qid);
-        if (chp)
+        if (chp) {
+                spin_lock_irqsave(&chp->comp_handler_lock, flag);
                 (*chp->ibcq.comp_handler)(&chp->ibcq, chp->ibcq.cq_context);
-        else
+                spin_unlock_irqrestore(&chp->comp_handler_lock, flag);
+        } else
                 PDBG("%s unknown cqid 0x%x\n", __func__, qid);
         return 0;
 }