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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: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel 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
This commit is contained in:
Toke Høiland-Jørgensen 2021-06-24 18:06:08 +02:00 committed by Daniel Borkmann
parent 7b6ee873ff
commit 2f1e432d33
1 changed files with 2 additions and 8 deletions
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10
drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
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@ -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 @@ read_again:
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: