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[bpf-next,v5,14/19] nfp: remove rcu_read_lock() around XDP program invocation

Message ID 20210624160609.292325-15-toke@redhat.com (mailing list archive)
State Accepted
Commit d5789621b658369b21bd13446bab8102cf75df65
Delegated to: BPF
Headers show
Series Clean up and document RCU-based object protection for XDP and TC BPF | expand

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netdev/tree_selection success Clearly marked for bpf-next
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netdev/cc_maintainers warning 16 maintainers not CCed: luc.vanoostenryck@gmail.com lorenzo@kernel.org gustavoars@kernel.org simon.horman@corigine.com yhs@fb.com kpsingh@kernel.org hawk@kernel.org andrii@kernel.org apais@linux.microsoft.com daniel@iogearbox.net oss-drivers@corigine.com ast@kernel.org john.fastabend@gmail.com songliubraving@fb.com davem@davemloft.net alexanderduyck@fb.com
netdev/source_inline success Was 0 now: 0
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netdev/module_param success Was 0 now: 0
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
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netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 14 lines checked
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Commit Message

Toke Høiland-Jørgensen June 24, 2021, 4:06 p.m. UTC 
The nfp 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.

While this is not actually an issue for the nfp driver because it doesn't
support XDP_REDIRECT (and thus doesn't call xdp_do_flush()), the
rcu_read_lock() is still unneeded. And 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: Simon Horman <simon.horman@netronome.com>
Cc: oss-drivers@netronome.com
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 drivers/net/ethernet/netronome/nfp/nfp_net_common.c | 2 --
 1 file changed, 2 deletions(-)
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Patch

diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
index eeb30680b4dc..5dfa4799c34f 100644
--- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
+++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
@@ -1819,7 +1819,6 @@  static int nfp_net_rx(struct nfp_net_rx_ring *rx_ring, int budget)
 	struct xdp_buff xdp;
 	int idx;
 
-	rcu_read_lock();
 	xdp_prog = READ_ONCE(dp->xdp_prog);
 	true_bufsz = xdp_prog ? PAGE_SIZE : dp->fl_bufsz;
 	xdp_init_buff(&xdp, PAGE_SIZE - NFP_NET_RX_BUF_HEADROOM,
@@ -2036,7 +2035,6 @@  static int nfp_net_rx(struct nfp_net_rx_ring *rx_ring, int budget)
 			if (!nfp_net_xdp_complete(tx_ring))
 				pkts_polled = budget;
 	}
-	rcu_read_unlock();
 
 	return pkts_polled;
 }