Re: [PATCH] bpf: return EOPNOTSUPP when JIT is needed and not possible

On Thu, Dec 09, 2021 at 11:05:18AM -0800, John Fastabend wrote:

Thadeu Lima de Souza Cascardo wrote:

quoted

When a CBPF program is JITed and CONFIG_BPF_JIT_ALWAYS_ON is enabled, and
the JIT fails, it would return ENOTSUPP, which is not a valid userspace
error code.  Instead, EOPNOTSUPP should be returned.

Fixes: 290af86629b2 ("bpf: introduce BPF_JIT_ALWAYS_ON config")
Signed-off-by: Thadeu Lima de Souza Cascardo <redacted>
---
 kernel/bpf/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index de3e5bc6781f..5c89bae0d6f9 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c

@@ -1931,7 +1931,7 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err)
 		fp = bpf_int_jit_compile(fp);
 		bpf_prog_jit_attempt_done(fp);
 		if (!fp->jited && jit_needed) {
-			*err = -ENOTSUPP;
+			*err = -EOPNOTSUPP;
 			return fp;
 		}
 	} else {

-- 
2.32.0

It seems BPF subsys returns ENOTSUPP in multiple places. This fixes one
paticular case and is user facing. Not sure we want to one-off fix them
here creating user facing changes over multiple kernel versions. On the
fence with this one curious to see what others think. Haven't apps
already adapted to the current convention or they don't care?

Similar issue was discussed in the past. See:
https://lore.kernel.org/netdev/20191204.125135.750458923752225025.davem@davemloft.net/ (local)