Re: [PATCH v4 bpf-next 01/15] bpf: Introduce any context BPF specific memory allocator.

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Mon, Aug 29, 2022 at 2:30 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> On 8/26/22 4:44 AM, Alexei Starovoitov wrote:
> [...]
> > +
> > +/* Called from BPF program or from sys_bpf syscall.
> > + * In both cases migration is disabled.
> > + */
> > +void notrace *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size)
> > +{
> > +     int idx;
> > +     void *ret;
> > +
> > +     if (!size)
> > +             return ZERO_SIZE_PTR;
> > +
> > +     idx = bpf_mem_cache_idx(size + LLIST_NODE_SZ);
> > +     if (idx < 0)
> > +             return NULL;
> > +
> > +     ret = unit_alloc(this_cpu_ptr(ma->caches)->cache + idx);
> > +     return !ret ? NULL : ret + LLIST_NODE_SZ;
> > +}
> > +
> > +void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr)
> > +{
> > +     int idx;
> > +
> > +     if (!ptr)
> > +             return;
> > +
> > +     idx = bpf_mem_cache_idx(__ksize(ptr - LLIST_NODE_SZ));
> > +     if (idx < 0)
> > +             return;
> > +
> > +     unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr);
> > +}
> > +
> > +void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma)
> > +{
> > +     void *ret;
> > +
> > +     ret = unit_alloc(this_cpu_ptr(ma->cache));
> > +     return !ret ? NULL : ret + LLIST_NODE_SZ;
> > +}
> > +
> > +void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
> > +{
> > +     if (!ptr)
> > +             return;
> > +
> > +     unit_free(this_cpu_ptr(ma->cache), ptr);
> > +}
>
> Looks like smp_processor_id() needs to be made aware that preemption might
> be ok just not migration to a different CPU?

ahh. migration is not disabled when map is freed from worker.
this_cpu_ptr above and local_irq_save shortly after need to happen
on the same cpu, so I'm thinking to add migrate_disable
to htab free path.