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ena: Remove rcu_read_lock() around XDP program invocation 

The ena 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: Saeed Bishara <saeedb@amazon.com>
Cc: Guy Tzalik <gtzalik@amazon.com>
Link: https://lore.kernel.org/bpf/20210624160609.292325-8-toke@redhat.com
This commit is contained in:
Toke Høiland-Jørgensen 2021-06-24 18:05:57 +02:00 committed by Daniel Borkmann
parent 77151ccf10
commit 0939e05378
1 changed files with 0 additions and 3 deletions
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3
drivers/net/ethernet/amazon/ena/ena_netdev.c
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@ -382,7 +382,6 @@ static int ena_xdp_execute(struct ena_ring *rx_ring, struct xdp_buff *xdp)
struct xdp_frame *xdpf;
u64 *xdp_stat;
rcu_read_lock();
xdp_prog = READ_ONCE(rx_ring->xdp_bpf_prog);
if (!xdp_prog)
@ -439,8 +438,6 @@ static int ena_xdp_execute(struct ena_ring *rx_ring, struct xdp_buff *xdp)
ena_increase_stat(xdp_stat, 1, &rx_ring->syncp);
out:
rcu_read_unlock();
return verdict;
}