intel: Remove rcu_read_lock() around XDP program invocation

The Intel drivers all have 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: NToke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Tested-by: Jesper Dangaard Brouer <brouer@redhat.com> # i40e
Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>
Cc: Tony Nguyen <anthony.l.nguyen@intel.com>
Cc: intel-wired-lan@lists.osuosl.org
Link: https://lore.kernel.org/bpf/20210624160609.292325-12-toke@redhat.com

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -2298,7 +2298,6 @@ static int i40e_run_xdp(struct i40e_ring *rx_ring, struct xdp_buff *xdp)
 	struct bpf_prog *xdp_prog;
 	u32 act;
 
-	rcu_read_lock();
 	xdp_prog = READ_ONCE(rx_ring->xdp_prog);
 
 	if (!xdp_prog)
@@ -2334,7 +2333,6 @@ static int i40e_run_xdp(struct i40e_ring *rx_ring, struct xdp_buff *xdp)
 		break;
 	}
 xdp_out:
-	rcu_read_unlock();
 	return result;
 }
 

drivers/net/ethernet/intel/i40e/i40e_xsk.c

@@ -153,7 +153,6 @@ static int i40e_run_xdp_zc(struct i40e_ring *rx_ring, struct xdp_buff *xdp)
 	struct bpf_prog *xdp_prog;
 	u32 act;
 
-	rcu_read_lock();
 	/* NB! xdp_prog will always be !NULL, due to the fact that
 	 * this path is enabled by setting an XDP program.
 	 */
@@ -164,7 +163,6 @@ static int i40e_run_xdp_zc(struct i40e_ring *rx_ring, struct xdp_buff *xdp)
 		err = xdp_do_redirect(rx_ring->netdev, xdp, xdp_prog);
 		if (err)
 			goto out_failure;
-		rcu_read_unlock();
 		return I40E_XDP_REDIR;
 	}
 
@@ -188,7 +186,6 @@ static int i40e_run_xdp_zc(struct i40e_ring *rx_ring, struct xdp_buff *xdp)
 		result = I40E_XDP_CONSUMED;
 		break;
 	}
-	rcu_read_unlock();
 	return result;
 }
 

drivers/net/ethernet/intel/ice/ice_txrx.c

@@ -1135,15 +1135,11 @@ int ice_clean_rx_irq(struct ice_ring *rx_ring, int budget)
 		xdp.frame_sz = ice_rx_frame_truesize(rx_ring, size);
 #endif
 
-		rcu_read_lock();
 		xdp_prog = READ_ONCE(rx_ring->xdp_prog);
-		if (!xdp_prog) {
-			rcu_read_unlock();
+		if (!xdp_prog)
 			goto construct_skb;
-		}
 
 		xdp_res = ice_run_xdp(rx_ring, &xdp, xdp_prog);
-		rcu_read_unlock();
 		if (!xdp_res)
 			goto construct_skb;
 		if (xdp_res & (ICE_XDP_TX | ICE_XDP_REDIR)) {

drivers/net/ethernet/intel/ice/ice_xsk.c

@@ -466,7 +466,6 @@ ice_run_xdp_zc(struct ice_ring *rx_ring, struct xdp_buff *xdp)
 	struct ice_ring *xdp_ring;
 	u32 act;
 
-	rcu_read_lock();
 	/* ZC patch is enabled only when XDP program is set,
 	 * so here it can not be NULL
 	 */
@@ -478,7 +477,6 @@ ice_run_xdp_zc(struct ice_ring *rx_ring, struct xdp_buff *xdp)
 		err = xdp_do_redirect(rx_ring->netdev, xdp, xdp_prog);
 		if (err)
 			goto out_failure;
-		rcu_read_unlock();
 		return ICE_XDP_REDIR;
 	}
 
@@ -503,7 +501,6 @@ ice_run_xdp_zc(struct ice_ring *rx_ring, struct xdp_buff *xdp)
 		break;
 	}
 
-	rcu_read_unlock();
 	return result;
 }
 

drivers/net/ethernet/intel/igb/igb_main.c

@@ -8381,7 +8381,6 @@ static struct sk_buff *igb_run_xdp(struct igb_adapter *adapter,
 	struct bpf_prog *xdp_prog;
 	u32 act;
 
-	rcu_read_lock();
 	xdp_prog = READ_ONCE(rx_ring->xdp_prog);
 
 	if (!xdp_prog)
@@ -8416,7 +8415,6 @@ static struct sk_buff *igb_run_xdp(struct igb_adapter *adapter,
 		break;
 	}
 xdp_out:
-	rcu_read_unlock();
 	return ERR_PTR(-result);
 }
 

drivers/net/ethernet/intel/igc/igc_main.c

@@ -2240,18 +2240,15 @@ static struct sk_buff *igc_xdp_run_prog(struct igc_adapter *adapter,
 	struct bpf_prog *prog;
 	int res;
 
-	rcu_read_lock();
-
 	prog = READ_ONCE(adapter->xdp_prog);
 	if (!prog) {
 		res = IGC_XDP_PASS;
-		goto unlock;
+		goto out;
 	}
 
 	res = __igc_xdp_run_prog(adapter, prog, xdp);
 
-unlock:
-	rcu_read_unlock();
+out:
 	return ERR_PTR(-res);
 }
 

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -2199,7 +2199,6 @@ static struct sk_buff *ixgbe_run_xdp(struct ixgbe_adapter *adapter,
 	struct xdp_frame *xdpf;
 	u32 act;
 
-	rcu_read_lock();
 	xdp_prog = READ_ONCE(rx_ring->xdp_prog);
 
 	if (!xdp_prog)
@@ -2237,7 +2236,6 @@ static struct sk_buff *ixgbe_run_xdp(struct ixgbe_adapter *adapter,
 		break;
 	}
 xdp_out:
-	rcu_read_unlock();
 	return ERR_PTR(-result);
 }
 

drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c

@@ -100,7 +100,6 @@ static int ixgbe_run_xdp_zc(struct ixgbe_adapter *adapter,
 	struct xdp_frame *xdpf;
 	u32 act;
 
-	rcu_read_lock();
 	xdp_prog = READ_ONCE(rx_ring->xdp_prog);
 	act = bpf_prog_run_xdp(xdp_prog, xdp);
 
@@ -108,7 +107,6 @@ static int ixgbe_run_xdp_zc(struct ixgbe_adapter *adapter,
 		err = xdp_do_redirect(rx_ring->netdev, xdp, xdp_prog);
 		if (err)
 			goto out_failure;
-		rcu_read_unlock();
 		return IXGBE_XDP_REDIR;
 	}
 
@@ -134,7 +132,6 @@ static int ixgbe_run_xdp_zc(struct ixgbe_adapter *adapter,
 		result = IXGBE_XDP_CONSUMED;
 		break;
 	}
-	rcu_read_unlock();
 	return result;
 }
 

drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c

@@ -1054,7 +1054,6 @@ static struct sk_buff *ixgbevf_run_xdp(struct ixgbevf_adapter *adapter,
 	struct bpf_prog *xdp_prog;
 	u32 act;
 
-	rcu_read_lock();
 	xdp_prog = READ_ONCE(rx_ring->xdp_prog);
 
 	if (!xdp_prog)
@@ -1082,7 +1081,6 @@ static struct sk_buff *ixgbevf_run_xdp(struct ixgbevf_adapter *adapter,
 		break;
 	}
 xdp_out:
-	rcu_read_unlock();
 	return ERR_PTR(-result);
 }