On Sat, Dec 18, 2021 at 9:25 PM Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote: > > 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. I'm still confused. Why does mark_btf_ld_reg() need to copy ref_obj_id ? It should keep it as zero. mark_btf_ld_reg() is used in deref only. The ref_obj_id is assigned by check_helper_call(). r2 = r0; will copy it, but r2 = r0->next; will keep r2->ref_obj_id as zero. > > 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. I don't understand why such logic is needed.
