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marvell: Remove rcu_read_lock() around XDP program invocation 

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.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Marcin Wojtas <mw@semihalf.com>
Link: https://lore.kernel.org/bpf/20210624160609.292325-13-toke@redhat.com
This commit is contained in:
Toke Høiland-Jørgensen 2021-06-24 18:06:02 +02:00 committed by Daniel Borkmann
parent 49589b23d5
commit 959ad7ec06
2 changed files with 0 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/net/ethernet/marvell/mvneta.c
View File

@ -2373,7 +2373,6 @@ 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 */
@ -2451,7 +2450,6 @@ next:
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);

4
drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
View File

@ -3881,8 +3881,6 @@ 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 */
@ -4028,8 +4026,6 @@ err_drop_frame:
mvpp2_bm_pool_put(port, pool, dma_addr, phys_addr);
}
rcu_read_unlock();
if (xdp_ret & MVPP2_XDP_REDIR)
xdp_do_flush_map();