IB/srp: Fix a race condition triggered by destroying a queue pair

At least LID reassignment can trigger a race condition in the SRP
initiator driver, namely the receive completion handler trying to
post a request on a QP during or after QP destruction and before
the CQ's have been destroyed. Avoid this race by modifying a QP
into the error state and by waiting until all receive completions
have been processed before destroying a QP.

Reported-by: Max Gurtuvoy <maxg@mellanox.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

2 files changed, 52 insertions, 9 deletions

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index aac844a6eef6..57b5ff1bbcb6 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -453,6 +453,41 @@ static struct srp_fr_pool *srp_alloc_fr_pool(struct srp_target_port *target)
                                   dev->max_pages_per_mr);
 }
 
+/**
+ * srp_destroy_qp() - destroy an RDMA queue pair
+ * @ch: SRP RDMA channel.
+ *
+ * Change a queue pair into the error state and wait until all receive
+ * completions have been processed before destroying it. This avoids that
+ * the receive completion handler can access the queue pair while it is
+ * being destroyed.
+ */
+static void srp_destroy_qp(struct srp_rdma_ch *ch)
+{
+        struct srp_target_port *target = ch->target;
+        static struct ib_qp_attr attr = { .qp_state = IB_QPS_ERR };
+        static struct ib_recv_wr wr = { .wr_id = SRP_LAST_WR_ID };
+        struct ib_recv_wr *bad_wr;
+        int ret;
+
+        /* Destroying a QP and reusing ch->done is only safe if not connected */
+        WARN_ON_ONCE(target->connected);
+
+        ret = ib_modify_qp(ch->qp, &attr, IB_QP_STATE);
+        WARN_ONCE(ret, "ib_cm_init_qp_attr() returned %d\n", ret);
+        if (ret)
+                goto out;
+
+        init_completion(&ch->done);
+        ret = ib_post_recv(ch->qp, &wr, &bad_wr);
+        WARN_ONCE(ret, "ib_post_recv() returned %d\n", ret);
+        if (ret == 0)
+                wait_for_completion(&ch->done);
+
+out:
+        ib_destroy_qp(ch->qp);
+}
+
 static int srp_create_ch_ib(struct srp_rdma_ch *ch)
 {
         struct srp_target_port *target = ch->target;
@@ -469,8 +504,9 @@ static int srp_create_ch_ib(struct srp_rdma_ch *ch)
         if (!init_attr)
                 return -ENOMEM;
 
+        /* + 1 for SRP_LAST_WR_ID */
         recv_cq = ib_create_cq(dev->dev, srp_recv_completion, NULL, ch,
-                               target->queue_size, ch->comp_vector);
+                               target->queue_size + 1, ch->comp_vector);
         if (IS_ERR(recv_cq)) {
                 ret = PTR_ERR(recv_cq);
                 goto err;
@@ -487,7 +523,7 @@ static int srp_create_ch_ib(struct srp_rdma_ch *ch)
 
         init_attr->event_handler       = srp_qp_event;
         init_attr->cap.max_send_wr     = m * target->queue_size;
-        init_attr->cap.max_recv_wr     = target->queue_size;
+        init_attr->cap.max_recv_wr     = target->queue_size + 1;
         init_attr->cap.max_recv_sge    = 1;
         init_attr->cap.max_send_sge    = 1;
         init_attr->sq_sig_type         = IB_SIGNAL_REQ_WR;
@@ -530,7 +566,7 @@ static int srp_create_ch_ib(struct srp_rdma_ch *ch)
         }
 
         if (ch->qp)
-                ib_destroy_qp(ch->qp);
+                srp_destroy_qp(ch);
         if (ch->recv_cq)
                 ib_destroy_cq(ch->recv_cq);
         if (ch->send_cq)
@@ -586,7 +622,7 @@ static void srp_free_ch_ib(struct srp_target_port *target,
                 if (ch->fmr_pool)
                         ib_destroy_fmr_pool(ch->fmr_pool);
         }
-        ib_destroy_qp(ch->qp);
+        srp_destroy_qp(ch);
         ib_destroy_cq(ch->send_cq);
         ib_destroy_cq(ch->recv_cq);
 
@@ -1883,8 +1919,15 @@ static void srp_tl_err_work(struct work_struct *work)
 }
 
 static void srp_handle_qp_err(u64 wr_id, enum ib_wc_status wc_status,
-                              bool send_err, struct srp_target_port *target)
+                              bool send_err, struct srp_rdma_ch *ch)
 {
+        struct srp_target_port *target = ch->target;
+
+        if (wr_id == SRP_LAST_WR_ID) {
+                complete(&ch->done);
+                return;
+        }
+
         if (target->connected && !target->qp_in_error) {
                 if (wr_id & LOCAL_INV_WR_ID_MASK) {
                         shost_printk(KERN_ERR, target->scsi_host, PFX
@@ -1915,8 +1958,7 @@ static void srp_recv_completion(struct ib_cq *cq, void *ch_ptr)
                 if (likely(wc.status == IB_WC_SUCCESS)) {
                         srp_handle_recv(ch, &wc);
                 } else {
-                        srp_handle_qp_err(wc.wr_id, wc.status, false,
-                                          ch->target);
+                        srp_handle_qp_err(wc.wr_id, wc.status, false, ch);
                 }
         }
 }
@@ -1932,8 +1974,7 @@ static void srp_send_completion(struct ib_cq *cq, void *ch_ptr)
                         iu = (struct srp_iu *) (uintptr_t) wc.wr_id;
                         list_add(&iu->list, &ch->free_tx);
                 } else {
-                        srp_handle_qp_err(wc.wr_id, wc.status, true,
-                                          ch->target);
+                        srp_handle_qp_err(wc.wr_id, wc.status, true, ch);
                 }
         }
 }
diff --git a/drivers/infiniband/ulp/srp/ib_srp.h b/drivers/infiniband/ulp/srp/ib_srp.h
index ca7c6f065434..a611556406ac 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.h
+++ b/drivers/infiniband/ulp/srp/ib_srp.h
@@ -70,6 +70,8 @@ enum {
 
         LOCAL_INV_WR_ID_MASK    = 1,
         FAST_REG_WR_ID_MASK     = 2,
+
+        SRP_LAST_WR_ID          = 0xfffffffcU,
 };
 
 enum srp_target_state {