On Sun, Dec 19, 2021 at 10:35:18AM IST, Alexei Starovoitov wrote: > On Sat, Dec 18, 2021 at 8:33 PM Kumar Kartikeya Dwivedi > <memxor@xxxxxxxxx> wrote: > > > > It is, but into parent_ref_obj_id, to match during release_reference. > > > > > Shouldn't r2 get a different ref_obj_id after r2 = r1->next ? > > > > It's ref_obj_id is still 0. > > > > Thinking about this more, we actually only need 1 extra bit of information in > > reg_state, not even a new member. We can simply copy ref_obj_id and set this > > bit, then we can reject this register during release but consider it during > > release_reference. > > It seems to me that this patch created the problem and it's trying > to fix it at the same time. > Yes, sort of. Maybe I need to improve the commit message? I give an example below, and the first half of commit explains that if we simply did copy ref_obj_id, it would lead to the case in the previous mail (same BTF ID ptr can be passed), so we need to do something different. Maybe that is what is confusing you. > mark_btf_ld_reg() shouldn't be copying ref_obj_id. > If it keeps it as zero the problem will not happen, no? It is copying it but writing it to parent_ref_obj_id. It keeps ref_obj_id as 0 for all deref pointers. r1 = acq(); // r1.ref = acquire_reference_state(); ref = N r2 = r1->a; // mark_btf_ld_reg -> copy r1.(ref ?: parent_ref) -> so r2.parent_ref = r1.ref r3 = r2->b; // mark_btf_ld_reg -> copy r2.(ref ?: parent_ref) -> so r3.parent_ref = r2.parent_ref r4 = r3->c; // mark_btf_ld_reg -> copy r3.(ref ?: parent_ref) -> so r4.parent_ref = r3.parent_ref rel(r1); // if (reg.ref == r1.ref || reg.parent_ref == r1.ref) invalidate(reg) As you see, mark_btf_ld_reg only ever writes to parent_ref_obj_id, not ref_obj_id. It just copies ref_obj_id when it is set, over parent_ref_obj_id, and only one of two can be set. -- Kartikeya
