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 <peppe.cavallaro@xxxxxx>
Cc: Alexandre Torgue <alexandre.torgue@xxxxxxxxxxx>
Cc: Jose Abreu <joabreu@xxxxxxxxxxxx>
Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
---
drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 10 ++--------
1 file changed, 2 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..08c4b999e1ba 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)
@@ -4696,17 +4695,14 @@ 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 +4972,8 @@ 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
