Commit 2f1e432d authored by Toke Høiland-Jørgensen's avatar Toke Høiland-Jørgensen Committed by Daniel Borkmann
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stmmac: Remove rcu_read_lock() around XDP program invocation 



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.

Signed-off-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Jose Abreu <joabreu@synopsys.com>
Link: https://lore.kernel.org/bpf/20210624160609.292325-19-toke@redhat.com
parent 7b6ee873

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

+2 −8
Original line number Diff line number Diff line
@@ -4651,7 +4651,6 @@ 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)
@@ -4693,17 +4692,14 @@ 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);

}
@@ -4973,10 +4969,8 @@ 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: