[PATCH bpf-next v2 15/16] stmmac: remove rcu_read_lock() around XDP program invocation
From: Toke Høiland-Jørgensen <hidden>
Date: 2021-06-15 14:55:18
Also in:
bpf
Subsystem:
networking drivers, stmmac ethernet driver, the rest · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
The stmmac driver has 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: Giuseppe Cavallaro <redacted> Cc: Alexandre Torgue <alexandre.torgue@foss.st.com> Cc: Jose Abreu <redacted> Signed-off-by: Toke Høiland-Jørgensen <redacted> --- drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index bf9fe25fed69..5dcc8a42abf9 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c@@ -4654,7 +4654,6 @@ static int stmmac_xdp_xmit_back(struct stmmac_priv *priv, return res; } -/* This function assumes rcu_read_lock() is held by the caller. */ static int __stmmac_xdp_run_prog(struct stmmac_priv *priv, struct bpf_prog *prog, struct xdp_buff *xdp)
@@ -4662,6 +4661,9 @@ static int __stmmac_xdp_run_prog(struct stmmac_priv *priv, u32 act; int res; + /* This code is invoked within a single NAPI poll cycle and thus under + * local_bh_disable(), which provides the needed RCU protection. + */ act = bpf_prog_run_xdp(prog, xdp); switch (act) { case XDP_PASS:
@@ -4696,17 +4698,14 @@ static struct sk_buff *stmmac_xdp_run_prog(struct stmmac_priv *priv, struct bpf_prog *prog; int res; - rcu_read_lock(); - prog = READ_ONCE(priv->xdp_prog); if (!prog) { res = STMMAC_XDP_PASS; - goto unlock; + goto out; } res = __stmmac_xdp_run_prog(priv, prog, xdp); -unlock: - rcu_read_unlock(); +out: return ERR_PTR(-res); }
@@ -4976,10 +4975,8 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue) buf->xdp->data_end = buf->xdp->data + buf1_len; xsk_buff_dma_sync_for_cpu(buf->xdp, rx_q->xsk_pool); - rcu_read_lock(); prog = READ_ONCE(priv->xdp_prog); res = __stmmac_xdp_run_prog(priv, prog, buf->xdp); - rcu_read_unlock(); switch (res) { case STMMAC_XDP_PASS:
--
2.31.1