On 2026/3/11 23:44, Alexei Starovoitov wrote:

On Wed, Mar 11, 2026 at 2:22 AM Kumar Kartikeya Dwivedi
[off-list ref] wrote:

quoted

[...]

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I agree but the main question is whether such a case is realistic, are
we going to have write_ctx programs tail calling this way?
Tail calls are already pretty rare, thinking more about it extension
programs are probably also broken wrt checks in this set.
bpf_check_attach_target is doing none of these things for
prog_extension = true. Nobody reported a problem, so I doubt anyone is
hitting this.
It probably also needs to be fixed.
Since you noticed it, we should close the gap conservatively for now,
and wait for a real use case to pop up before enabling this one-way.

+1
tail_calls in general hopefully will be deprecated soon.
As soon as we have support for indirect calls there won't be any reason
for tail calls to exist. (other than not breaking current users).
We definitely don't want to open it up further.
So the simplest fix.

Got it.

Will follow the both-ways check approach in the next revision.

Will apply the conservative check to extension programs using another
patch series, after verifying the potential issues for them.

Thanks,
Leon