When running an XDP bpf_prog on the remote CPU in cpumap code
then we must disable the direct return optimization that
xdp_return can perform for mem_type page_pool. This optimization
assumes code is still executing under RX-NAPI of the original
receiving CPU, which isn't true on this remote CPU.
The cpumap code already disabled this via helpers
xdp_set_return_frame_no_direct() and xdp_clear_return_frame_no_direct(),
but the scope didn't include xdp_do_flush().
When doing XDP_REDIRECT towards e.g devmap this causes the
function bq_xmit_all() to run with direct return optimization
enabled. This can lead to hard to find bugs. The issue
only happens when bq_xmit_all() cannot ndo_xdp_xmit all
frames and them frees them via xdp_return_frame_rx_napi().
Fix by expanding scope to include xdp_do_flush().
Fixes: 11941f8a8536 ("bpf: cpumap: Implement generic cpumap")
Found-by: Dragos Tatulea <dtatulea@xxxxxxxxxx>
Reported-by: Chris Arges <carges@xxxxxxxxxxxxxx>
Signed-off-by: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
---
kernel/bpf/cpumap.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index b2b7b8ec2c2a..c46360b27871 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -186,7 +186,6 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
struct xdp_buff xdp;
int i, nframes = 0;
- xdp_set_return_frame_no_direct();
xdp.rxq = &rxq;
for (i = 0; i < n; i++) {
@@ -231,7 +230,6 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
}
}
- xdp_clear_return_frame_no_direct();
stats->pass += nframes;
return nframes;
@@ -255,6 +253,7 @@ static void cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
rcu_read_lock();
bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
+ xdp_set_return_frame_no_direct();
ret->xdp_n = cpu_map_bpf_prog_run_xdp(rcpu, frames, ret->xdp_n, stats);
if (unlikely(ret->skb_n))
@@ -264,6 +263,7 @@ static void cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
if (stats->redirect)
xdp_do_flush();
+ xdp_clear_return_frame_no_direct();
bpf_net_ctx_clear(bpf_net_ctx);
rcu_read_unlock();
