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sfc: Remove rcu_read_lock() around XDP program invocation

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The sfc 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>
Acked-by: Edward Cree <ecree.xilinx@gmail.com>
Cc: Martin Habets <habetsm.xilinx@gmail.com>
Link: https://lore.kernel.org/bpf/20210624160609.292325-17-toke@redhat.com
This commit is contained in:
Toke Høiland-Jørgensen 2021-06-24 18:06:06 +02:00 committed by Daniel Borkmann
parent 4415db6ca8
commit 4eb14e3fc6
1 changed files with 2 additions and 7 deletions
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9
drivers/net/ethernet/sfc/rx.c
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@ -260,18 +260,14 @@ static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel,
s16 offset;
int err;
rcu_read_lock();
xdp_prog = rcu_dereference(efx->xdp_prog);
if (!xdp_prog) {
rcu_read_unlock();
xdp_prog = rcu_dereference_bh(efx->xdp_prog);
if (!xdp_prog)
return true;
}
rx_queue = efx_channel_get_rx_queue(channel);
if (unlikely(channel->rx_pkt_n_frags > 1)) {
/* We can't do XDP on fragmented packets - drop. */
rcu_read_unlock();
efx_free_rx_buffers(rx_queue, rx_buf,
channel->rx_pkt_n_frags);
if (net_ratelimit())
@ -296,7 +292,6 @@ static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel,
rx_buf->len, false);
xdp_act = bpf_prog_run_xdp(xdp_prog, &xdp);
rcu_read_unlock();
offset = (u8 *)xdp.data - *ehp;