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SubjectRe: [PATCH v2 2/6] ixgbe: Fix incorrect RCU API usage
On Sat, Feb 23, 2019 at 01:34:30AM -0500, Joel Fernandes (Google) wrote:
> Recently, I added an RCU annotation check in rcu_assign_pointer. This
> caused a sparse error to be reported by the ixgbe driver.
>
> Further looking, it seems the adapter->xdp_prog pointer is not annotated
> with __rcu. Annonating it fixed the error, but caused a bunch of other
> warnings.
>
> This patch tries to fix all warnings by using RCU API properly. This
> makes sense to do because not using RCU properly can result in various
> hard to find bugs. This is a best effort fix and is only build tested.
> The sparse errors and warnings go away with the change. I request
> maintainers / developers in this area to review / test it properly.
>
> The sparse error fixed is:
> ixgbe_main.c:10256:25: error: incompatible types in comparison expression
>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

From an RCU perspective:

Reviewed-by: Paul E. McKenney <paulmck@linux.ibm.com>

> ---
> drivers/net/ethernet/intel/ixgbe/ixgbe.h | 4 ++--
> drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 15 ++++++++++-----
> 2 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe.h b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
> index 08d85e336bd4..3b14daf27516 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe.h
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
> @@ -311,7 +311,7 @@ struct ixgbe_ring {
> struct ixgbe_ring *next; /* pointer to next ring in q_vector */
> struct ixgbe_q_vector *q_vector; /* backpointer to host q_vector */
> struct net_device *netdev; /* netdev ring belongs to */
> - struct bpf_prog *xdp_prog;
> + struct bpf_prog __rcu *xdp_prog;
> struct device *dev; /* device for DMA mapping */
> void *desc; /* descriptor ring memory */
> union {
> @@ -560,7 +560,7 @@ struct ixgbe_adapter {
> unsigned long active_vlans[BITS_TO_LONGS(VLAN_N_VID)];
> /* OS defined structs */
> struct net_device *netdev;
> - struct bpf_prog *xdp_prog;
> + struct bpf_prog __rcu *xdp_prog;
> struct pci_dev *pdev;
> struct mii_bus *mii_bus;
>
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index daff8183534b..408a312aa6ba 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -2199,7 +2199,7 @@ static struct sk_buff *ixgbe_run_xdp(struct ixgbe_adapter *adapter,
> u32 act;
>
> rcu_read_lock();
> - xdp_prog = READ_ONCE(rx_ring->xdp_prog);
> + xdp_prog = rcu_dereference(rx_ring->xdp_prog);
>
> if (!xdp_prog)
> goto xdp_out;
> @@ -6547,7 +6547,7 @@ int ixgbe_setup_rx_resources(struct ixgbe_adapter *adapter,
> rx_ring->queue_index) < 0)
> goto err;
>
> - rx_ring->xdp_prog = adapter->xdp_prog;
> + rcu_assign_pointer(rx_ring->xdp_prog, adapter->xdp_prog);
>
> return 0;
> err:
> @@ -10246,7 +10246,8 @@ static int ixgbe_xdp_setup(struct net_device *dev, struct bpf_prog *prog)
> if (nr_cpu_ids > MAX_XDP_QUEUES)
> return -ENOMEM;
>
> - old_prog = xchg(&adapter->xdp_prog, prog);
> + old_prog = rcu_access_pointer(adapter->xdp_prog);
> + rcu_assign_pointer(adapter->xdp_prog, prog);
>
> /* If transitioning XDP modes reconfigure rings */
> if (!!prog != !!old_prog) {
> @@ -10271,13 +10272,17 @@ static int ixgbe_xdp_setup(struct net_device *dev, struct bpf_prog *prog)
> static int ixgbe_xdp(struct net_device *dev, struct netdev_bpf *xdp)
> {
> struct ixgbe_adapter *adapter = netdev_priv(dev);
> + struct bpf_prog *prog;
>
> switch (xdp->command) {
> case XDP_SETUP_PROG:
> return ixgbe_xdp_setup(dev, xdp->prog);
> case XDP_QUERY_PROG:
> - xdp->prog_id = adapter->xdp_prog ?
> - adapter->xdp_prog->aux->id : 0;
> + rcu_read_lock();
> + prog = rcu_dereference(adapter->xdp_prog);
> + xdp->prog_id = prog ? prog->aux->id : 0;
> + rcu_read_unlock();
> +
> return 0;
> case XDP_QUERY_XSK_UMEM:
> return ixgbe_xsk_umem_query(adapter, &xdp->xsk.umem,
> --
> 2.21.0.rc0.258.g878e2cd30e-goog
>

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