Messages in this thread | | | From | Alexander Potapenko <> | Date | Thu, 10 Sep 2020 18:19:10 +0200 | Subject | Re: [PATCH RFC 01/10] mm: add Kernel Electric-Fence infrastructure |
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On Thu, Sep 10, 2020 at 5:43 PM Dmitry Vyukov <dvyukov@google.com> wrote:
> > + /* Calculate address for this allocation. */ > > + if (right) > > + meta->addr += PAGE_SIZE - size; > > + meta->addr = ALIGN_DOWN(meta->addr, cache->align); > > I would move this ALIGN_DOWN under the (right) if. > Do I understand it correctly that it will work, but we expect it to do > nothing for !right? If cache align is >PAGE_SIZE, nothing good will > happen anyway, right? > The previous 2 lines look like part of the same calculation -- "figure > out the addr for the right case".
Yes, makes sense.
> > + > > + schedule_delayed_work(&kfence_timer, 0); > > + WRITE_ONCE(kfence_enabled, true); > > Can toggle_allocation_gate run before we set kfence_enabled? If yes, > it can break. If not, it's still somewhat confusing.
Correct, it should go after we enable KFENCE. We'll fix that in v2.
> > +void __kfence_free(void *addr) > > +{ > > + struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); > > + > > + if (unlikely(meta->cache->flags & SLAB_TYPESAFE_BY_RCU)) > > This may deserve a comment as to why we apply rcu on object level > whereas SLAB_TYPESAFE_BY_RCU means slab level only.
Sorry, what do you mean by "slab level"? SLAB_TYPESAFE_BY_RCU means we have to wait for possible RCU accesses in flight before freeing objects from that slab - that's basically what we are doing here below:
> > + call_rcu(&meta->rcu_head, rcu_guarded_free); > > + else > > + kfence_guarded_free(addr, meta); > > +}
> > +void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta) > > +{ > > + const int size = abs(meta->size); > > This negative encoding is somewhat confusing. We do lots of abs, but > do we even look at the sign anywhere? I can't find any use that is not > abs.
I think initially there was a reason for this, but now we don't seem to use it anywhere. Nice catch!
Alex
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