RDMA/iw_cxgb4: Fix refcount underflow while destroying cqs.

Previous atomic increment/decrement logic expects the atomic count to be
'0' after the final decrement.

Replacing atomic count with refcount does not allow that, as
refcount_dec() considers count of 1 as underflow and triggers a kernel
splat.

Fix the current refcount logic by using the usual pattern of decrementing
the refcount and test if it is '0' on the final deref in
c4iw_destroy_cq(). Use wait_for_completion() instead of wait_event().

Fixes: 7183451f846d ("RDMA/cxgb4: Use refcount_t instead of atomic_t for reference counting")
Link: https://lore.kernel.org/r/1628167412-12114-1-git-send-email-dakshaja@chelsio.com
Signed-off-by: Dakshaja Uppalapati <dakshaja@chelsio.com>
Reviewed-by: Potnuri Bharat Teja <bharat@chelsio.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/infiniband/hw/cxgb4/cq.c b/drivers/infiniband/hw/cxgb4/cq.c
index 6c8c910..c7e8d7b 100644 (file)
--- a/drivers/infiniband/hw/cxgb4/cq.c
+++ b/drivers/infiniband/hw/cxgb4/cq.c
@@ -967,6 +967,12 @@ int c4iw_poll_cq(struct ib_cq *ibcq, int num_entries, struct ib_wc *wc)
        return !err || err == -ENODATA ? npolled : err;
 }
 
+void c4iw_cq_rem_ref(struct c4iw_cq *chp)
+{
+       if (refcount_dec_and_test(&chp->refcnt))
+               complete(&chp->cq_rel_comp);
+}
+
 int c4iw_destroy_cq(struct ib_cq *ib_cq, struct ib_udata *udata)
 {
        struct c4iw_cq *chp;
@@ -976,8 +982,8 @@ int c4iw_destroy_cq(struct ib_cq *ib_cq, struct ib_udata *udata)
        chp = to_c4iw_cq(ib_cq);
 
        xa_erase_irq(&chp->rhp->cqs, chp->cq.cqid);
-       refcount_dec(&chp->refcnt);
-       wait_event(chp->wait, !refcount_read(&chp->refcnt));
+       c4iw_cq_rem_ref(chp);
+       wait_for_completion(&chp->cq_rel_comp);
 
        ucontext = rdma_udata_to_drv_context(udata, struct c4iw_ucontext,
                                             ibucontext);
@@ -1081,7 +1087,7 @@ int c4iw_create_cq(struct ib_cq *ibcq, const struct ib_cq_init_attr *attr,
        spin_lock_init(&chp->lock);
        spin_lock_init(&chp->comp_handler_lock);
        refcount_set(&chp->refcnt, 1);
-       init_waitqueue_head(&chp->wait);
+       init_completion(&chp->cq_rel_comp);
        ret = xa_insert_irq(&rhp->cqs, chp->cq.cqid, chp, GFP_KERNEL);
        if (ret)
                goto err_destroy_cq;

diff --git a/drivers/infiniband/hw/cxgb4/ev.c b/drivers/infiniband/hw/cxgb4/ev.c
index 7798d09..34211a5 100644 (file)
--- a/drivers/infiniband/hw/cxgb4/ev.c
+++ b/drivers/infiniband/hw/cxgb4/ev.c
@@ -213,8 +213,7 @@ void c4iw_ev_dispatch(struct c4iw_dev *dev, struct t4_cqe *err_cqe)
                break;
        }
 done:
-       if (refcount_dec_and_test(&chp->refcnt))
-               wake_up(&chp->wait);
+       c4iw_cq_rem_ref(chp);
        c4iw_qp_rem_ref(&qhp->ibqp);
 out:
        return;
@@ -234,8 +233,7 @@ int c4iw_ev_handler(struct c4iw_dev *dev, u32 qid)
                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);
-               if (refcount_dec_and_test(&chp->refcnt))
-                       wake_up(&chp->wait);
+               c4iw_cq_rem_ref(chp);
        } else {
                pr_debug("unknown cqid 0x%x\n", qid);
                xa_unlock_irqrestore(&dev->cqs, flag);

diff --git a/drivers/infiniband/hw/cxgb4/iw_cxgb4.h b/drivers/infiniband/hw/cxgb4/iw_cxgb4.h
index 3883af3..ac5f581 100644 (file)
--- a/drivers/infiniband/hw/cxgb4/iw_cxgb4.h
+++ b/drivers/infiniband/hw/cxgb4/iw_cxgb4.h
@@ -428,7 +428,7 @@ struct c4iw_cq {
        spinlock_t lock;
        spinlock_t comp_handler_lock;
        refcount_t refcnt;
-       wait_queue_head_t wait;
+       struct completion cq_rel_comp;
        struct c4iw_wr_wait *wr_waitp;
 };
 
@@ -979,6 +979,7 @@ struct ib_mr *c4iw_reg_user_mr(struct ib_pd *pd, u64 start,
 struct ib_mr *c4iw_get_dma_mr(struct ib_pd *pd, int acc);
 int c4iw_dereg_mr(struct ib_mr *ib_mr, struct ib_udata *udata);
 int c4iw_destroy_cq(struct ib_cq *ib_cq, struct ib_udata *udata);
+void c4iw_cq_rem_ref(struct c4iw_cq *chp);
 int c4iw_create_cq(struct ib_cq *ibcq, const struct ib_cq_init_attr *attr,
                   struct ib_udata *udata);
 int c4iw_arm_cq(struct ib_cq *ibcq, enum ib_cq_notify_flags flags);