@@ -2370,7 +2370,6 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
/* Get number of received packets */
rx_todo = mvneta_rxq_busy_desc_num_get(pp, rxq);
- rcu_read_lock();
xdp_prog = READ_ONCE(pp->xdp_prog);
/* Fairness NAPI loop */
@@ -2421,6 +2420,10 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
goto next;
}
+ /* This code is invoked within a single NAPI poll cycle and thus
+ * under local_bh_disable(), which provides the needed RCU
+ * protection.
+ */
if (xdp_prog &&
mvneta_run_xdp(pp, rxq, xdp_prog, &xdp_buf, frame_sz, &ps))
goto next;
@@ -2448,7 +2451,6 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
xdp_buf.data_hard_start = NULL;
sinfo.nr_frags = 0;
}
- rcu_read_unlock();
if (xdp_buf.data_hard_start)
mvneta_xdp_put_buff(pp, rxq, &xdp_buf, &sinfo, -1);
@@ -3852,8 +3852,6 @@ static int mvpp2_rx(struct mvpp2_port *port, struct napi_struct *napi,
int rx_done = 0;
u32 xdp_ret = 0;
- rcu_read_lock();
-
xdp_prog = READ_ONCE(port->xdp_prog);
/* Get number of received packets and clamp the to-do */
@@ -3925,6 +3923,10 @@ static int mvpp2_rx(struct mvpp2_port *port, struct napi_struct *napi,
MVPP2_MH_SIZE + MVPP2_SKB_HEADROOM,
rx_bytes, false);
+ /* This code is invoked within a single NAPI poll cycle
+ * and thus under local_bh_disable(), which provides the
+ * needed RCU protection.
+ */
ret = mvpp2_run_xdp(port, xdp_prog, &xdp, pp, &ps);
if (ret) {
@@ -3988,8 +3990,6 @@ static int mvpp2_rx(struct mvpp2_port *port, struct napi_struct *napi,
mvpp2_bm_pool_put(port, pool, dma_addr, phys_addr);
}
- rcu_read_unlock();
-
if (xdp_ret & MVPP2_XDP_REDIR)
xdp_do_flush_map();
The mvneta and mvpp2 drivers 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. Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com> Cc: Marcin Wojtas <mw@semihalf.com> Cc: Russell King <linux@armlinux.org.uk> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com> --- drivers/net/ethernet/marvell/mvneta.c | 6 ++++-- drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 8 ++++---- 2 files changed, 8 insertions(+), 6 deletions(-)