* [PATCH bpf-next v4 09/19] thunderx: remove rcu_read_lock() around XDP program invocation
[not found] <20210623110727.221922-1-toke@redhat.com>
@ 2021-06-23 11:07 ` Toke Høiland-Jørgensen
0 siblings, 0 replies; only message in thread
From: Toke Høiland-Jørgensen @ 2021-06-23 11:07 UTC (permalink / raw)
To: bpf, netdev
Cc: Martin KaFai Lau, Hangbin Liu, Jesper Dangaard Brouer,
Magnus Karlsson, Paul E . McKenney, Jakub Kicinski,
Toke Høiland-Jørgensen, Sunil Goutham, linux-arm-kernel
The thunderx 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.
Cc: Sunil Goutham <sgoutham@marvell.com>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
drivers/net/ethernet/cavium/thunder/nicvf_main.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/drivers/net/ethernet/cavium/thunder/nicvf_main.c b/drivers/net/ethernet/cavium/thunder/nicvf_main.c
index c33b4e837515..e2b290135fd9 100644
--- a/drivers/net/ethernet/cavium/thunder/nicvf_main.c
+++ b/drivers/net/ethernet/cavium/thunder/nicvf_main.c
@@ -555,9 +555,7 @@ static inline bool nicvf_xdp_rx(struct nicvf *nic, struct bpf_prog *prog,
xdp_prepare_buff(&xdp, hard_start, data - hard_start, len, false);
orig_data = xdp.data;
- rcu_read_lock();
action = bpf_prog_run_xdp(prog, &xdp);
- rcu_read_unlock();
len = xdp.data_end - xdp.data;
/* Check if XDP program has changed headers */
--
2.32.0
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