qede: Remove rcu_read_lock() around XDP program invocation

The qede 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: Ariel Elior <aelior@marvell.com>
Cc: gr-everest-linux-l2@marvell.com
Link: https://lore.kernel.org/bpf/20210624160609.292325-16-toke@redhat.com

diff --git a/drivers/net/ethernet/qlogic/qede/qede_fp.c b/drivers/net/ethernet/qlogic/qede/qede_fp.c
index 8e150dd..065e900 100644 (file)
--- a/drivers/net/ethernet/qlogic/qede/qede_fp.c
+++ b/drivers/net/ethernet/qlogic/qede/qede_fp.c
@@ -1089,13 +1089,7 @@ static bool qede_rx_xdp(struct qede_dev *edev,
        xdp_prepare_buff(&xdp, page_address(bd->data), *data_offset,
                         *len, false);
 
-       /* Queues always have a full reset currently, so for the time
-        * being until there's atomic program replace just mark read
-        * side for map helpers.
-        */
-       rcu_read_lock();
        act = bpf_prog_run_xdp(prog, &xdp);
-       rcu_read_unlock();
 
        /* Recalculate, as XDP might have changed the headers */
        *data_offset = xdp.data - xdp.data_hard_start;