diff mbox series

[bpf-next,v5,16/19] sfc: remove rcu_read_lock() around XDP program invocation

Message ID 20210624160609.292325-17-toke@redhat.com (mailing list archive)
State Accepted
Commit 4eb14e3fc6197b7205069ed4e2b31eafa11a0697
Delegated to: BPF
Headers show
Series Clean up and document RCU-based object protection for XDP and TC BPF | expand

Checks

Context Check Description
netdev/cover_letter success Link
netdev/fixes_present success Link
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netdev/tree_selection success Clearly marked for bpf-next
netdev/subject_prefix success Link
netdev/cc_maintainers warning 9 maintainers not CCed: yhs@fb.com kpsingh@kernel.org daniel@iogearbox.net andrii@kernel.org hawk@kernel.org ast@kernel.org john.fastabend@gmail.com songliubraving@fb.com davem@davemloft.net
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, 27 lines checked
netdev/build_allmodconfig_warn success Errors and warnings before: 0 this patch: 0
netdev/header_inline success Link

Commit Message

Toke Høiland-Jørgensen June 24, 2021, 4:06 p.m. UTC 
The sfc 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: Edward Cree <ecree.xilinx@gmail.com>
Cc: Martin Habets <habetsm.xilinx@gmail.com>
Acked-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 drivers/net/ethernet/sfc/rx.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)
diff mbox series

Patch

diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 17b8119c48e5..606750938b89 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -260,18 +260,14 @@  static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel,
 	s16 offset;
 	int err;
 
-	rcu_read_lock();
-	xdp_prog = rcu_dereference(efx->xdp_prog);
-	if (!xdp_prog) {
-		rcu_read_unlock();
+	xdp_prog = rcu_dereference_bh(efx->xdp_prog);
+	if (!xdp_prog)
 		return true;
-	}
 
 	rx_queue = efx_channel_get_rx_queue(channel);
 
 	if (unlikely(channel->rx_pkt_n_frags > 1)) {
 		/* We can't do XDP on fragmented packets - drop. */
-		rcu_read_unlock();
 		efx_free_rx_buffers(rx_queue, rx_buf,
 				    channel->rx_pkt_n_frags);
 		if (net_ratelimit())
@@ -296,7 +292,6 @@  static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel,
 			 rx_buf->len, false);
 
 	xdp_act = bpf_prog_run_xdp(xdp_prog, &xdp);
-	rcu_read_unlock();
 
 	offset = (u8 *)xdp.data - *ehp;