RE: [PATCH bpf-next v2 07/16] freescale: remove rcu_read_lock() around XDP program invocation
From: Camelia Alexandra Groza <hidden>
Date: 2021-06-16 14:58:41
Also in:
netdev
-----Original Message----- From: Toke Høiland-Jørgensen <redacted> Sent: Tuesday, June 15, 2021 17:55 To: bpf@vger.kernel.org; netdev@vger.kernel.org Cc: Martin KaFai Lau <redacted>; Hangbin Liu <redacted>; Jesper Dangaard Brouer [off-list ref]; Magnus Karlsson [off-list ref]; Paul E . McKenney [off-list ref]; Jakub Kicinski [off-list ref]; Toke Høiland-Jørgensen [off-list ref]; Madalin Bucur [off-list ref]; Ioana Ciornei [off-list ref]; Ioana Ciocoi Radulescu [off-list ref] 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@nxp.com> Cc: Ioana Ciornei <ioana.ciornei@nxp.com> Cc: Ioana Radulescu <redacted> Signed-off-by: Toke Høiland-Jørgensen <redacted> ---
Reviewed-by: Camelia Groza <redacted> Thanks!
quoted hunk ↗ jump to hunk
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.cb/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.cb/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