Re: [RFC PATCH v3 04/12] netdev: support binding dma-buf to netdevice

From: Mina Almasry <almasrymina@google.com>
To: David Wei <dw@davidwei.uk>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org,
	linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linaro-mm-sig@lists.linaro.org,
	"David S. Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"Ilias Apalodimas" <ilias.apalodimas@linaro.org>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"David Ahern" <dsahern@kernel.org>,
	"Willem de Bruijn" <willemdebruijn.kernel@gmail.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	"Christian König" <christian.koenig@amd.com>,
	"Shakeel Butt" <shakeelb@google.com>,
	"Jeroen de Borst" <jeroendb@google.com>,
	"Praveen Kaligineedi" <pkaligineedi@google.com>,
	"Willem de Bruijn" <willemb@google.com>,
	"Kaiyuan Zhang" <kaiyuanz@google.com>,
	"Pavel Begunkov" <asml.silence@gmail.com>
Subject: Re: [RFC PATCH v3 04/12] netdev: support binding dma-buf to netdevice
Date: Wed, 8 Nov 2023 18:25:56 -0800	[thread overview]
Message-ID: <CAHS8izO1p==W+ppDqwEE9ugehN4OL9J3+fdrY+UJch9s8uShOg@mail.gmail.com> (raw)
In-Reply-To: <7769b74d-dd23-41de-8e11-434a0acabf72@davidwei.uk>

On Wed, Nov 8, 2023 at 3:47 PM David Wei <dw@davidwei.uk> wrote:
>
> On 2023-11-05 18:44, Mina Almasry wrote:
> > Add a netdev_dmabuf_binding struct which represents the
> > dma-buf-to-netdevice binding. The netlink API will bind the dma-buf to
> > rx queues on the netdevice. On the binding, the dma_buf_attach
> > & dma_buf_map_attachment will occur. The entries in the sg_table from
> > mapping will be inserted into a genpool to make it ready
> > for allocation.
> >
> > The chunks in the genpool are owned by a dmabuf_chunk_owner struct which
> > holds the dma-buf offset of the base of the chunk and the dma_addr of
> > the chunk. Both are needed to use allocations that come from this chunk.
> >
> > We create a new type that represents an allocation from the genpool:
> > page_pool_iov. We setup the page_pool_iov allocation size in the
> > genpool to PAGE_SIZE for simplicity: to match the PAGE_SIZE normally
> > allocated by the page pool and given to the drivers.
> >
> > The user can unbind the dmabuf from the netdevice by closing the netlink
> > socket that established the binding. We do this so that the binding is
> > automatically unbound even if the userspace process crashes.
> >
> > The binding and unbinding leaves an indicator in struct netdev_rx_queue
> > that the given queue is bound, but the binding doesn't take effect until
> > the driver actually reconfigures its queues, and re-initializes its page
> > pool.
> >
> > The netdev_dmabuf_binding struct is refcounted, and releases its
> > resources only when all the refs are released.
> >
> > Signed-off-by: Willem de Bruijn <willemb@google.com>
> > Signed-off-by: Kaiyuan Zhang <kaiyuanz@google.com>
> > Signed-off-by: Mina Almasry <almasrymina@google.com>
> >
> > ---
> >
> > RFC v3:
> > - Support multi rx-queue binding
> >
> > ---
> >  include/linux/netdevice.h     |  80 ++++++++++++++
> >  include/net/netdev_rx_queue.h |   1 +
> >  include/net/page_pool/types.h |  27 +++++
> >  net/core/dev.c                | 203 ++++++++++++++++++++++++++++++++++
> >  net/core/netdev-genl.c        | 116 ++++++++++++++++++-
> >  5 files changed, 425 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index b8bf669212cc..eeeda849115c 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -52,6 +52,8 @@
> >  #include <net/net_trackers.h>
> >  #include <net/net_debug.h>
> >  #include <net/dropreason-core.h>
> > +#include <linux/xarray.h>
> > +#include <linux/refcount.h>
> >
> >  struct netpoll_info;
> >  struct device;
> > @@ -808,6 +810,84 @@ bool rps_may_expire_flow(struct net_device *dev, u16 rxq_index, u32 flow_id,
> >  #endif
> >  #endif /* CONFIG_RPS */
> >
> > +struct netdev_dmabuf_binding {
> > +     struct dma_buf *dmabuf;
> > +     struct dma_buf_attachment *attachment;
> > +     struct sg_table *sgt;
> > +     struct net_device *dev;
> > +     struct gen_pool *chunk_pool;
> > +
> > +     /* The user holds a ref (via the netlink API) for as long as they want
> > +      * the binding to remain alive. Each page pool using this binding holds
> > +      * a ref to keep the binding alive. Each allocated page_pool_iov holds a
> > +      * ref.
> > +      *
> > +      * The binding undos itself and unmaps the underlying dmabuf once all
> > +      * those refs are dropped and the binding is no longer desired or in
> > +      * use.
> > +      */
> > +     refcount_t ref;
> > +
> > +     /* The portid of the user that owns this binding. Used for netlink to
> > +      * notify us of the user dropping the bind.
> > +      */
> > +     u32 owner_nlportid;
> > +
> > +     /* The list of bindings currently active. Used for netlink to notify us
> > +      * of the user dropping the bind.
> > +      */
> > +     struct list_head list;
> > +
> > +     /* rxq's this binding is active on. */
> > +     struct xarray bound_rxq_list;
> > +};
> > +
> > +#ifdef CONFIG_DMA_SHARED_BUFFER
> > +void __netdev_devmem_binding_free(struct netdev_dmabuf_binding *binding);
> > +int netdev_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,
> > +                    struct netdev_dmabuf_binding **out);
> > +void netdev_unbind_dmabuf(struct netdev_dmabuf_binding *binding);
> > +int netdev_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
> > +                             struct netdev_dmabuf_binding *binding);
> > +#else
> > +static inline void
> > +__netdev_devmem_binding_free(struct netdev_dmabuf_binding *binding)
> > +{
> > +}
> > +
> > +static inline int netdev_bind_dmabuf(struct net_device *dev,
> > +                                  unsigned int dmabuf_fd,
> > +                                  struct netdev_dmabuf_binding **out)
> > +{
> > +     return -EOPNOTSUPP;
> > +}
> > +static inline void netdev_unbind_dmabuf(struct netdev_dmabuf_binding *binding)
> > +{
> > +}
> > +
> > +static inline int
> > +netdev_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
> > +                         struct netdev_dmabuf_binding *binding)
> > +{
> > +     return -EOPNOTSUPP;
> > +}
> > +#endif
> > +
> > +static inline void
> > +netdev_devmem_binding_get(struct netdev_dmabuf_binding *binding)
> > +{
> > +     refcount_inc(&binding->ref);
> > +}
> > +
> > +static inline void
> > +netdev_devmem_binding_put(struct netdev_dmabuf_binding *binding)
> > +{
> > +     if (!refcount_dec_and_test(&binding->ref))
> > +             return;
> > +
> > +     __netdev_devmem_binding_free(binding);
> > +}
> > +
> >  /* XPS map type and offset of the xps map within net_device->xps_maps[]. */
> >  enum xps_map_type {
> >       XPS_CPUS = 0,
> > diff --git a/include/net/netdev_rx_queue.h b/include/net/netdev_rx_queue.h
> > index cdcafb30d437..1bfcf60a145d 100644
> > --- a/include/net/netdev_rx_queue.h
> > +++ b/include/net/netdev_rx_queue.h
> > @@ -21,6 +21,7 @@ struct netdev_rx_queue {
> >  #ifdef CONFIG_XDP_SOCKETS
> >       struct xsk_buff_pool            *pool;
> >  #endif
> > +     struct netdev_dmabuf_binding *binding;
>
> @Pavel - They are using struct netdev_rx_queue to hold the binding,
> which is an object that holds the state and is mapped 1:1 to an rxq.
> This object is similar to our "interface queue". I wonder if we should
> re-visit using this generic struct, instead of driver specific structs
> e.g. bnxt_rx_ring_info?
>
> >  } ____cacheline_aligned_in_smp;
> >
> >  /*
> > diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
> > index d4bea053bb7e..64386325d965 100644
> > --- a/include/net/page_pool/types.h
> > +++ b/include/net/page_pool/types.h
> > @@ -133,6 +133,33 @@ struct pp_memory_provider_ops {
> >       bool (*release_page)(struct page_pool *pool, struct page *page);
> >  };
> >
> > +/* page_pool_iov support */
> > +
> > +/* Owner of the dma-buf chunks inserted into the gen pool. Each scatterlist
> > + * entry from the dmabuf is inserted into the genpool as a chunk, and needs
> > + * this owner struct to keep track of some metadata necessary to create
> > + * allocations from this chunk.
> > + */
> > +struct dmabuf_genpool_chunk_owner {
> > +     /* Offset into the dma-buf where this chunk starts.  */
> > +     unsigned long base_virtual;
> > +
> > +     /* dma_addr of the start of the chunk.  */
> > +     dma_addr_t base_dma_addr;
> > +
> > +     /* Array of page_pool_iovs for this chunk. */
> > +     struct page_pool_iov *ppiovs;
> > +     size_t num_ppiovs;
> > +
> > +     struct netdev_dmabuf_binding *binding;
> > +};
> > +
> > +struct page_pool_iov {
> > +     struct dmabuf_genpool_chunk_owner *owner;
> > +
> > +     refcount_t refcount;
> > +};
> > +
> >  struct page_pool {
> >       struct page_pool_params p;
> >
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index a37a932a3e14..c8c3709d42c8 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -153,6 +153,9 @@
> >  #include <linux/prandom.h>
> >  #include <linux/once_lite.h>
> >  #include <net/netdev_rx_queue.h>
> > +#include <linux/genalloc.h>
> > +#include <linux/dma-buf.h>
> > +#include <net/page_pool/types.h>
> >
> >  #include "dev.h"
> >  #include "net-sysfs.h"
> > @@ -2040,6 +2043,206 @@ static int call_netdevice_notifiers_mtu(unsigned long val,
> >       return call_netdevice_notifiers_info(val, &info.info);
> >  }
> >
> > +/* Device memory support */
> > +
> > +#ifdef CONFIG_DMA_SHARED_BUFFER
> > +static void netdev_devmem_free_chunk_owner(struct gen_pool *genpool,
> > +                                        struct gen_pool_chunk *chunk,
> > +                                        void *not_used)
> > +{
> > +     struct dmabuf_genpool_chunk_owner *owner = chunk->owner;
> > +
> > +     kvfree(owner->ppiovs);
> > +     kfree(owner);
> > +}
> > +
> > +void __netdev_devmem_binding_free(struct netdev_dmabuf_binding *binding)
> > +{
> > +     size_t size, avail;
> > +
> > +     gen_pool_for_each_chunk(binding->chunk_pool,
> > +                             netdev_devmem_free_chunk_owner, NULL);
> > +
> > +     size = gen_pool_size(binding->chunk_pool);
> > +     avail = gen_pool_avail(binding->chunk_pool);
> > +
> > +     if (!WARN(size != avail, "can't destroy genpool. size=%lu, avail=%lu",
> > +               size, avail))
> > +             gen_pool_destroy(binding->chunk_pool);
> > +
> > +     dma_buf_unmap_attachment(binding->attachment, binding->sgt,
> > +                              DMA_BIDIRECTIONAL);
> > +     dma_buf_detach(binding->dmabuf, binding->attachment);
> > +     dma_buf_put(binding->dmabuf);
> > +     kfree(binding);
> > +}
> > +
> > +void netdev_unbind_dmabuf(struct netdev_dmabuf_binding *binding)
> > +{
> > +     struct netdev_rx_queue *rxq;
> > +     unsigned long xa_idx;
> > +
> > +     if (!binding)
> > +             return;
> > +
> > +     list_del_rcu(&binding->list);
> > +
> > +     xa_for_each(&binding->bound_rxq_list, xa_idx, rxq)
> > +             if (rxq->binding == binding)
> > +                     /* We hold the rtnl_lock while binding/unbinding
> > +                      * dma-buf, so we can't race with another thread that
> > +                      * is also modifying this value. However, the driver
> > +                      * may read this config while it's creating its
> > +                      * rx-queues. WRITE_ONCE() here to match the
> > +                      * READ_ONCE() in the driver.
> > +                      */
> > +                     WRITE_ONCE(rxq->binding, NULL);
> > +
> > +     netdev_devmem_binding_put(binding);
> > +}
> > +
> > +int netdev_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
> > +                             struct netdev_dmabuf_binding *binding)
> > +{
> > +     struct netdev_rx_queue *rxq;
> > +     u32 xa_idx;
> > +     int err;
> > +
> > +     rxq = __netif_get_rx_queue(dev, rxq_idx);
> > +
> > +     if (rxq->binding)
> > +             return -EEXIST;
> > +
> > +     err = xa_alloc(&binding->bound_rxq_list, &xa_idx, rxq, xa_limit_32b,
> > +                    GFP_KERNEL);
> > +     if (err)
> > +             return err;
> > +
> > +     /*We hold the rtnl_lock while binding/unbinding dma-buf, so we can't
> > +      * race with another thread that is also modifying this value. However,
> > +      * the driver may read this config while it's creating its * rx-queues.
> > +      * WRITE_ONCE() here to match the READ_ONCE() in the driver.
> > +      */
> > +     WRITE_ONCE(rxq->binding, binding);
> > +
> > +     return 0;
> > +}
> > +
> > +int netdev_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,
> > +                    struct netdev_dmabuf_binding **out)
>
> I'm not entirely familiar with the Netlink API. Mina, do you know if we
> can call into netdev_bind_dmabuf or netdev_nl_bind_rx_doit directly,
> without needing to call send/recv on a Netlink socket? We likely want
> io_uring to do the registration of a dmabuf fd and keep ownership over
> it.
>

You can likely call into netdev_bind_dmabuf(), but not
netdev_nl_bind_rx_doit. The latter is very netlink specific.

> > +{
> > +     struct netdev_dmabuf_binding *binding;
> > +     struct scatterlist *sg;
> > +     struct dma_buf *dmabuf;
> > +     unsigned int sg_idx, i;
> > +     unsigned long virtual;
> > +     int err;
> > +
> > +     if (!capable(CAP_NET_ADMIN))
> > +             return -EPERM;
> > +
> > +     dmabuf = dma_buf_get(dmabuf_fd);
> > +     if (IS_ERR_OR_NULL(dmabuf))
> > +             return -EBADFD;
> > +
> > +     binding = kzalloc_node(sizeof(*binding), GFP_KERNEL,
> > +                            dev_to_node(&dev->dev));
> > +     if (!binding) {
> > +             err = -ENOMEM;
> > +             goto err_put_dmabuf;
> > +     }
> > +
> > +     xa_init_flags(&binding->bound_rxq_list, XA_FLAGS_ALLOC);
> > +
> > +     refcount_set(&binding->ref, 1);
> > +
> > +     binding->dmabuf = dmabuf;
> > +
> > +     binding->attachment = dma_buf_attach(binding->dmabuf, dev->dev.parent);
> > +     if (IS_ERR(binding->attachment)) {
> > +             err = PTR_ERR(binding->attachment);
> > +             goto err_free_binding;
> > +     }
> > +
> > +     binding->sgt = dma_buf_map_attachment(binding->attachment,
> > +                                           DMA_BIDIRECTIONAL);
> > +     if (IS_ERR(binding->sgt)) {
> > +             err = PTR_ERR(binding->sgt);
> > +             goto err_detach;
> > +     }
> > +
> > +     /* For simplicity we expect to make PAGE_SIZE allocations, but the
> > +      * binding can be much more flexible than that. We may be able to
> > +      * allocate MTU sized chunks here. Leave that for future work...
> > +      */
> > +     binding->chunk_pool = gen_pool_create(PAGE_SHIFT,
> > +                                           dev_to_node(&dev->dev));
> > +     if (!binding->chunk_pool) {
> > +             err = -ENOMEM;
> > +             goto err_unmap;
> > +     }
> > +
> > +     virtual = 0;
> > +     for_each_sgtable_dma_sg(binding->sgt, sg, sg_idx) {
> > +             dma_addr_t dma_addr = sg_dma_address(sg);
> > +             struct dmabuf_genpool_chunk_owner *owner;
> > +             size_t len = sg_dma_len(sg);
> > +             struct page_pool_iov *ppiov;
> > +
> > +             owner = kzalloc_node(sizeof(*owner), GFP_KERNEL,
> > +                                  dev_to_node(&dev->dev));
> > +             owner->base_virtual = virtual;
> > +             owner->base_dma_addr = dma_addr;
> > +             owner->num_ppiovs = len / PAGE_SIZE;
> > +             owner->binding = binding;
> > +
> > +             err = gen_pool_add_owner(binding->chunk_pool, dma_addr,
> > +                                      dma_addr, len, dev_to_node(&dev->dev),
> > +                                      owner);
> > +             if (err) {
> > +                     err = -EINVAL;
> > +                     goto err_free_chunks;
> > +             }
> > +
> > +             owner->ppiovs = kvmalloc_array(owner->num_ppiovs,
> > +                                            sizeof(*owner->ppiovs),
> > +                                            GFP_KERNEL);
> > +             if (!owner->ppiovs) {
> > +                     err = -ENOMEM;
> > +                     goto err_free_chunks;
> > +             }
> > +
> > +             for (i = 0; i < owner->num_ppiovs; i++) {
> > +                     ppiov = &owner->ppiovs[i];
> > +                     ppiov->owner = owner;
> > +                     refcount_set(&ppiov->refcount, 1);
> > +             }
> > +
> > +             dma_addr += len;
> > +             virtual += len;
> > +     }
> > +
> > +     *out = binding;
> > +
> > +     return 0;
> > +
> > +err_free_chunks:
> > +     gen_pool_for_each_chunk(binding->chunk_pool,
> > +                             netdev_devmem_free_chunk_owner, NULL);
> > +     gen_pool_destroy(binding->chunk_pool);
> > +err_unmap:
> > +     dma_buf_unmap_attachment(binding->attachment, binding->sgt,
> > +                              DMA_BIDIRECTIONAL);
> > +err_detach:
> > +     dma_buf_detach(dmabuf, binding->attachment);
> > +err_free_binding:
> > +     kfree(binding);
> > +err_put_dmabuf:
> > +     dma_buf_put(dmabuf);
> > +     return err;
> > +}
> > +#endif
> > +
> >  #ifdef CONFIG_NET_INGRESS
> >  static DEFINE_STATIC_KEY_FALSE(ingress_needed_key);
> >
> > diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> > index 59d3d512d9cc..2c2a62593217 100644
> > --- a/net/core/netdev-genl.c
> > +++ b/net/core/netdev-genl.c
> > @@ -129,10 +129,89 @@ int netdev_nl_dev_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
> >       return skb->len;
> >  }
> >
> > -/* Stub */
> > +static LIST_HEAD(netdev_rbinding_list);
> > +
> >  int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
> >  {
> > -     return 0;
> > +     struct netdev_dmabuf_binding *out_binding;
> > +     u32 ifindex, dmabuf_fd, rxq_idx;
> > +     struct net_device *netdev;
> > +     struct sk_buff *rsp;
> > +     int rem, err = 0;
> > +     void *hdr;
> > +     struct nlattr *attr;
> > +
> > +     if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_DEV_IFINDEX) ||
> > +         GENL_REQ_ATTR_CHECK(info, NETDEV_A_BIND_DMABUF_DMABUF_FD) ||
> > +         GENL_REQ_ATTR_CHECK(info, NETDEV_A_BIND_DMABUF_QUEUES))
> > +             return -EINVAL;
> > +
> > +     ifindex = nla_get_u32(info->attrs[NETDEV_A_DEV_IFINDEX]);
> > +     dmabuf_fd = nla_get_u32(info->attrs[NETDEV_A_BIND_DMABUF_DMABUF_FD]);
> > +
> > +     rtnl_lock();
> > +
> > +     netdev = __dev_get_by_index(genl_info_net(info), ifindex);
> > +     if (!netdev) {
> > +             err = -ENODEV;
> > +             goto err_unlock;
> > +     }
> > +
> > +     err = netdev_bind_dmabuf(netdev, dmabuf_fd, &out_binding);
> > +     if (err)
> > +             goto err_unlock;
> > +
> > +     nla_for_each_attr(attr, genlmsg_data(info->genlhdr),
> > +                       genlmsg_len(info->genlhdr), rem) {
> > +             switch (nla_type(attr)) {
> > +             case NETDEV_A_BIND_DMABUF_QUEUES:
> > +                     rxq_idx = nla_get_u32(attr);
> > +
> > +                     if (rxq_idx >= netdev->num_rx_queues) {
> > +                             err = -ERANGE;
> > +                             goto err_unbind;
> > +                     }
> > +
> > +                     err = netdev_bind_dmabuf_to_queue(netdev, rxq_idx,
> > +                                                       out_binding);
> > +                     if (err)
> > +                             goto err_unbind;
> > +
> > +                     break;
> > +             default:
> > +                     break;
> > +             }
> > +     }
> > +
> > +     out_binding->owner_nlportid = info->snd_portid;
> > +     list_add_rcu(&out_binding->list, &netdev_rbinding_list);
> > +
> > +     rsp = genlmsg_new(GENLMSG_DEFAULT_SIZE, GFP_KERNEL);
> > +     if (!rsp) {
> > +             err = -ENOMEM;
> > +             goto err_unbind;
> > +     }
> > +
> > +     hdr = genlmsg_put(rsp, info->snd_portid, info->snd_seq,
> > +                       &netdev_nl_family, 0, info->genlhdr->cmd);
> > +     if (!hdr) {
> > +             err = -EMSGSIZE;
> > +             goto err_genlmsg_free;
> > +     }
> > +
> > +     genlmsg_end(rsp, hdr);
> > +
> > +     rtnl_unlock();
> > +
> > +     return genlmsg_reply(rsp, info);
> > +
> > +err_genlmsg_free:
> > +     nlmsg_free(rsp);
> > +err_unbind:
> > +     netdev_unbind_dmabuf(out_binding);
> > +err_unlock:
> > +     rtnl_unlock();
> > +     return err;
> >  }
> >
> >  static int netdev_genl_netdevice_event(struct notifier_block *nb,
> > @@ -155,10 +234,37 @@ static int netdev_genl_netdevice_event(struct notifier_block *nb,
> >       return NOTIFY_OK;
> >  }
> >
> > +static int netdev_netlink_notify(struct notifier_block *nb, unsigned long state,
> > +                              void *_notify)
> > +{
> > +     struct netlink_notify *notify = _notify;
> > +     struct netdev_dmabuf_binding *rbinding;
> > +
> > +     if (state != NETLINK_URELEASE || notify->protocol != NETLINK_GENERIC)
> > +             return NOTIFY_DONE;
> > +
> > +     rcu_read_lock();
> > +
> > +     list_for_each_entry_rcu(rbinding, &netdev_rbinding_list, list) {
> > +             if (rbinding->owner_nlportid == notify->portid) {
> > +                     netdev_unbind_dmabuf(rbinding);
> > +                     break;
> > +             }
> > +     }
> > +
> > +     rcu_read_unlock();
> > +
> > +     return NOTIFY_OK;
> > +}
> > +
> >  static struct notifier_block netdev_genl_nb = {
> >       .notifier_call  = netdev_genl_netdevice_event,
> >  };
> >
> > +static struct notifier_block netdev_netlink_notifier = {
> > +     .notifier_call = netdev_netlink_notify,
> > +};
>
> Is this mechamism what cleans up TCP devmem in case userspace crashes
> and the associated Netlink socket is closed?
>

Correct.

> > +
> >  static int __init netdev_genl_init(void)
> >  {
> >       int err;
> > @@ -171,8 +277,14 @@ static int __init netdev_genl_init(void)
> >       if (err)
> >               goto err_unreg_ntf;
> >
> > +     err = netlink_register_notifier(&netdev_netlink_notifier);
> > +     if (err)
> > +             goto err_unreg_family;
> > +
> >       return 0;
> >
> > +err_unreg_family:
> > +     genl_unregister_family(&netdev_nl_family);
> >  err_unreg_ntf:
> >       unregister_netdevice_notifier(&netdev_genl_nb);
> >       return err;

-- 
Thanks,
Mina