bpf, xdp: drop rcu_read_lock from bpf_prog_run_xdp and move to caller

After 326fe02d1ed6 ("net/mlx4_en: protect ring->xdp_prog with rcu_read_lock"),
the rcu_read_lock() in bpf_prog_run_xdp() is superfluous, since callers
need to hold rcu_read_lock() already to make sure BPF program doesn't
get released in the background.

Thus, drop it from bpf_prog_run_xdp(), as it can otherwise be misleading.
Still keeping the bpf_prog_run_xdp() is useful as it allows for grepping
in XDP supported drivers and to keep the typecheck on the context intact.
For mlx4, this means we don't have a double rcu_read_lock() anymore. nfp can
just make use of bpf_prog_run_xdp(), too. For qede, just move rcu_read_lock()
out of the helper. When the driver gets atomic replace support, this will
move to call-sites eventually.

mlx5 needs actual fixing as it has the same issue as described already in
326fe02d1ed6 ("net/mlx4_en: protect ring->xdp_prog with rcu_read_lock"),
that is, we're under RCU bh at this time, BPF programs are released via
call_rcu(), and call_rcu() != call_rcu_bh(), so we need to properly mark
read side as programs can get xchg()'ed in mlx5e_xdp_set() without queue
reset.

Fixes: 86994156c736 ("net/mlx5e: XDP fast RX drop bpf programs support")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 9 deletions

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 7ba644626553..97338134398f 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -498,16 +498,16 @@ static inline u32 bpf_prog_run_clear_cb(const struct bpf_prog *prog,
 	return BPF_PROG_RUN(prog, skb);
 }
 
-static inline u32 bpf_prog_run_xdp(const struct bpf_prog *prog,
-				   struct xdp_buff *xdp)
+static __always_inline u32 bpf_prog_run_xdp(const struct bpf_prog *prog,
+					    struct xdp_buff *xdp)
 {
-	u32 ret;
-
-	rcu_read_lock();
-	ret = BPF_PROG_RUN(prog, xdp);
-	rcu_read_unlock();
-
-	return ret;
+	/* Caller needs to hold rcu_read_lock() (!), otherwise program
+	 * can be released while still running, or map elements could be
+	 * freed early while still having concurrent users. XDP fastpath
+	 * already takes rcu_read_lock() when fetching the program, so
+	 * it's not necessary here anymore.
+	 */
+	return BPF_PROG_RUN(prog, xdp);
 }
 
 static inline unsigned int bpf_prog_size(unsigned int proglen)