> -----Original Message-----
> From: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> Sent: Tuesday, June 15, 2021 17:55
> To: bpf@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx
> Cc: Martin KaFai Lau <kafai@xxxxxx>; Hangbin Liu <liuhangbin@xxxxxxxxx>;
> Jesper Dangaard Brouer <brouer@xxxxxxxxxx>; Magnus Karlsson
> <magnus.karlsson@xxxxxxxxx>; Paul E . McKenney <paulmck@xxxxxxxxxx>;
> Jakub Kicinski <kuba@xxxxxxxxxx>; Toke Høiland-Jørgensen
> <toke@xxxxxxxxxx>; Madalin Bucur <madalin.bucur@xxxxxxx>; Ioana
> Ciornei <ioana.ciornei@xxxxxxx>; Ioana Ciocoi Radulescu
> <ruxandra.radulescu@xxxxxxx>
> Subject: [PATCH bpf-next v2 07/16] freescale: remove rcu_read_lock()
> around XDP program invocation
>
> The dpaa and dpaa2 drivers have rcu_read_lock()/rcu_read_unlock() pairs
> around XDP program invocations. However, the actual lifetime of the objects
> referred by the XDP program invocation is longer, all the way through to
> the call to xdp_do_flush(), making the scope of the rcu_read_lock() too
> small. This turns out to be harmless because it all happens in a single
> NAPI poll cycle (and thus under local_bh_disable()), but it makes the
> rcu_read_lock() misleading.
>
> Rather than extend the scope of the rcu_read_lock(), just get rid of it
> entirely. With the addition of RCU annotations to the XDP_REDIRECT map
> types that take bh execution into account, lockdep even understands this to
> be safe, so there's really no reason to keep it around.
>
> Cc: Madalin Bucur <madalin.bucur@xxxxxxx>
> Cc: Ioana Ciornei <ioana.ciornei@xxxxxxx>
> Cc: Ioana Radulescu <ruxandra.radulescu@xxxxxxx>
> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> ---
Reviewed-by: Camelia Groza <camelia.groza@xxxxxxx>
Thanks!
> drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 11 ++++-------
> drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c | 6 +++---
> 2 files changed, 7 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> index 177c020bf34a..98fdcbde687a 100644
> --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> @@ -2558,13 +2558,9 @@ static u32 dpaa_run_xdp(struct dpaa_priv *priv,
> struct qm_fd *fd, void *vaddr,
> u32 xdp_act;
> int err;
>
> - rcu_read_lock();
> -
> xdp_prog = READ_ONCE(priv->xdp_prog);
> - if (!xdp_prog) {
> - rcu_read_unlock();
> + if (!xdp_prog)
> return XDP_PASS;
> - }
>
> xdp_init_buff(&xdp, DPAA_BP_RAW_SIZE -
> DPAA_TX_PRIV_DATA_SIZE,
> &dpaa_fq->xdp_rxq);
> @@ -2585,6 +2581,9 @@ static u32 dpaa_run_xdp(struct dpaa_priv *priv,
> struct qm_fd *fd, void *vaddr,
> }
> #endif
>
> + /* This code is invoked within a single NAPI poll cycle and thus under
> + * local_bh_disable(), which provides the needed RCU protection.
> + */
> xdp_act = bpf_prog_run_xdp(xdp_prog, &xdp);
>
> /* Update the length and the offset of the FD */
> @@ -2638,8 +2637,6 @@ static u32 dpaa_run_xdp(struct dpaa_priv *priv,
> struct qm_fd *fd, void *vaddr,
> break;
> }
>
> - rcu_read_unlock();
> -
> return xdp_act;
> }
>
> diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> index 8433aa730c42..964d85c9e37d 100644
> --- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> +++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> @@ -352,8 +352,6 @@ static u32 dpaa2_eth_run_xdp(struct dpaa2_eth_priv
> *priv,
> u32 xdp_act = XDP_PASS;
> int err, offset;
>
> - rcu_read_lock();
> -
> xdp_prog = READ_ONCE(ch->xdp.prog);
> if (!xdp_prog)
> goto out;
> @@ -363,6 +361,9 @@ static u32 dpaa2_eth_run_xdp(struct dpaa2_eth_priv
> *priv,
> xdp_prepare_buff(&xdp, vaddr + offset, XDP_PACKET_HEADROOM,
> dpaa2_fd_get_len(fd), false);
>
> + /* This code is invoked within a single NAPI poll cycle and thus under
> + * local_bh_disable(), which provides the needed RCU protection.
> + */
> xdp_act = bpf_prog_run_xdp(xdp_prog, &xdp);
>
> /* xdp.data pointer may have changed */
> @@ -414,7 +415,6 @@ static u32 dpaa2_eth_run_xdp(struct dpaa2_eth_priv
> *priv,
>
> ch->xdp.res |= xdp_act;
> out:
> - rcu_read_unlock();
> return xdp_act;
> }
>
> --
> 2.31.1
