Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote: > Guys, it seems that we have a lot of code using SLAB_TYPESAFE_BY_RCU cache without constructor. > I think it's nearly impossible to use that combination without having bugs. > It's either you don't really need the SLAB_TYPESAFE_BY_RCU, or you need to have a constructor in kmem_cache. > > Could you guys, please, verify your code if it's really need SLAB_TYPSAFE or constructor? > > E.g. the netlink code look extremely suspicious: > > /* > * Do not use kmem_cache_zalloc(), as this cache uses > * SLAB_TYPESAFE_BY_RCU. > */ > ct = kmem_cache_alloc(nf_conntrack_cachep, gfp); > if (ct == NULL) > goto out; > > spin_lock_init(&ct->lock); > > If nf_conntrack_cachep objects really used in rcu typesafe manner, than 'ct' returned by kmem_cache_alloc might still be > in use by another cpu. So we just reinitialize spin_lock used by someone else? That would be a bug, nf_conn objects are reference counted. spinlock can only be used after object had its refcount incremented. lookup operation on nf_conn object: 1. compare keys 2. attempt to obtain refcount (using _not_zero version) 3. compare keys again after refcount was obtained if any of that fails, nf_conn candidate is skipped.
