On Fri, Dec 22, 2023 at 7:12 AM Dmitrii Dolgov <9erthalion6@xxxxxxxxx> wrote: > > Currently, it's not allowed to attach an fentry/fexit prog to another > one fentry/fexit. At the same time it's not uncommon to see a tracing > program with lots of logic in use, and the attachment limitation > prevents usage of fentry/fexit for performance analysis (e.g. with > "bpftool prog profile" command) in this case. An example could be > falcosecurity libs project that uses tp_btf tracing programs. > > Following the corresponding discussion [1], the reason for that is to > avoid tracing progs call cycles without introducing more complex > solutions. But currently it seems impossible to load and attach tracing > programs in a way that will form such a cycle. The limitation is coming > from the fact that attach_prog_fd is specified at the prog load (thus > making it impossible to attach to a program loaded after it in this > way), as well as tracing progs not implementing link_detach. > > Replace "no same type" requirement with verification that no more than > one level of attachment nesting is allowed. In this way only one > fentry/fexit program could be attached to another fentry/fexit to cover > profiling use case, and still no cycle could be formed. To implement, > add a new field into bpf_prog_aux to track nested attachment for tracing > programs. > > [1]: https://lore.kernel.org/bpf/20191108064039.2041889-16-ast@xxxxxxxxxx/ > > Acked-by: Jiri Olsa <olsajiri@xxxxxxxxx> > Signed-off-by: Dmitrii Dolgov <9erthalion6@xxxxxxxxx> Acked-by: Song Liu <song@xxxxxxxxxx>
