Howdy-
> On Aug 18, 2020, at 8:05 AM, Leon Romanovsky <leon@xxxxxxxxxx> wrote:
>
> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
>
> In almost all cases rdma_accept() is called under the handler_mutex by
> ULPs from their handler callbacks. The one exception was ucma which did
> not get the handler_mutex.
It turns out that the RPC/RDMA server also does not invoke rdma_accept()
from its CM event handler.
See net/sunrpc/xprtrdma/svc_rdma_transport.c:svc_rdma_accept()
When lock debugging is enabled, the lockdep assertion in rdma_accept()
fires on every RPC/RDMA connection.
I'm not quite sure what to do about this.
> To improve the understand-ability of the locking scheme obtain the mutex
> for ucma as well.
>
> This improves how ucma works by allowing it to directly use handler_mutex
> for some of its internal locking against the handler callbacks intead of
> the global file->mut lock.
>
> There does not seem to be a serious bug here, other than a DISCONNECT event
> can be delivered concurrently with accept succeeding.
>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxxxx>
> ---
> drivers/infiniband/core/cma.c | 25 ++++++++++++++++++++++---
> drivers/infiniband/core/ucma.c | 12 ++++++++----
> include/rdma/rdma_cm.h | 5 +++++
> 3 files changed, 35 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
> index 26de0dab60bb..78641858abe2 100644
> --- a/drivers/infiniband/core/cma.c
> +++ b/drivers/infiniband/core/cma.c
> @@ -4154,14 +4154,15 @@ static int cma_send_sidr_rep(struct rdma_id_private *id_priv,
> int __rdma_accept(struct rdma_cm_id *id, struct rdma_conn_param *conn_param,
> const char *caller)
> {
> - struct rdma_id_private *id_priv;
> + struct rdma_id_private *id_priv =
> + container_of(id, struct rdma_id_private, id);
> int ret;
>
> - id_priv = container_of(id, struct rdma_id_private, id);
> + lockdep_assert_held(&id_priv->handler_mutex);
>
> rdma_restrack_set_task(&id_priv->res, caller);
>
> - if (!cma_comp(id_priv, RDMA_CM_CONNECT))
> + if (READ_ONCE(id_priv->state) != RDMA_CM_CONNECT)
> return -EINVAL;
>
> if (!id->qp && conn_param) {
> @@ -4214,6 +4215,24 @@ int __rdma_accept_ece(struct rdma_cm_id *id, struct rdma_conn_param *conn_param,
> }
> EXPORT_SYMBOL(__rdma_accept_ece);
>
> +void rdma_lock_handler(struct rdma_cm_id *id)
> +{
> + struct rdma_id_private *id_priv =
> + container_of(id, struct rdma_id_private, id);
> +
> + mutex_lock(&id_priv->handler_mutex);
> +}
> +EXPORT_SYMBOL(rdma_lock_handler);
> +
> +void rdma_unlock_handler(struct rdma_cm_id *id)
> +{
> + struct rdma_id_private *id_priv =
> + container_of(id, struct rdma_id_private, id);
> +
> + mutex_unlock(&id_priv->handler_mutex);
> +}
> +EXPORT_SYMBOL(rdma_unlock_handler);
> +
> int rdma_notify(struct rdma_cm_id *id, enum ib_event_type event)
> {
> struct rdma_id_private *id_priv;
> diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c
> index dd12931f3038..add1ece38739 100644
> --- a/drivers/infiniband/core/ucma.c
> +++ b/drivers/infiniband/core/ucma.c
> @@ -1162,16 +1162,20 @@ static ssize_t ucma_accept(struct ucma_file *file, const char __user *inbuf,
>
> if (cmd.conn_param.valid) {
> ucma_copy_conn_param(ctx->cm_id, &conn_param, &cmd.conn_param);
> - mutex_lock(&file->mut);
> mutex_lock(&ctx->mutex);
> + rdma_lock_handler(ctx->cm_id);
> ret = __rdma_accept_ece(ctx->cm_id, &conn_param, NULL, &ece);
> - mutex_unlock(&ctx->mutex);
> - if (!ret)
> + if (!ret) {
> + /* The uid must be set atomically with the handler */
> ctx->uid = cmd.uid;
> - mutex_unlock(&file->mut);
> + }
> + rdma_unlock_handler(ctx->cm_id);
> + mutex_unlock(&ctx->mutex);
> } else {
> mutex_lock(&ctx->mutex);
> + rdma_lock_handler(ctx->cm_id);
> ret = __rdma_accept_ece(ctx->cm_id, NULL, NULL, &ece);
> + rdma_unlock_handler(ctx->cm_id);
> mutex_unlock(&ctx->mutex);
> }
> ucma_put_ctx(ctx);
> diff --git a/include/rdma/rdma_cm.h b/include/rdma/rdma_cm.h
> index cf5da2ae49bf..c1334c9a7aa8 100644
> --- a/include/rdma/rdma_cm.h
> +++ b/include/rdma/rdma_cm.h
> @@ -253,6 +253,8 @@ int rdma_listen(struct rdma_cm_id *id, int backlog);
> int __rdma_accept(struct rdma_cm_id *id, struct rdma_conn_param *conn_param,
> const char *caller);
>
> +void rdma_lock_handler(struct rdma_cm_id *id);
> +void rdma_unlock_handler(struct rdma_cm_id *id);
> int __rdma_accept_ece(struct rdma_cm_id *id, struct rdma_conn_param *conn_param,
> const char *caller, struct rdma_ucm_ece *ece);
>
> @@ -270,6 +272,9 @@ int __rdma_accept_ece(struct rdma_cm_id *id, struct rdma_conn_param *conn_param,
> * In the case of error, a reject message is sent to the remote side and the
> * state of the qp associated with the id is modified to error, such that any
> * previously posted receive buffers would be flushed.
> + *
> + * This function is for use by kernel ULPs and must be called from under the
> + * handler callback.
> */
> #define rdma_accept(id, conn_param) \
> __rdma_accept((id), (conn_param), KBUILD_MODNAME)
> --
> 2.26.2
>
--
Chuck Lever
