Em Thu, Sep 20, 2018 at 10:44:24AM +0200, Peter Zijlstra escreveu:
> On Wed, Sep 19, 2018 at 03:39:34PM -0700, Alexei Starovoitov wrote:
> > void bpf_prog_kallsyms_del(struct bpf_prog *fp)
> > {
> > + unsigned long symbol_start, symbol_end;
> > + /* mmap_record.filename cannot be NULL and has to be u64 aligned */
> > + char buf[sizeof(u64)] = {};
> > +
> > if (!bpf_prog_kallsyms_candidate(fp))
> > return;
> >
> > spin_lock_bh(&bpf_lock);
> > bpf_prog_ksym_node_del(fp->aux);
> > spin_unlock_bh(&bpf_lock);
> > + bpf_get_prog_addr_region(fp, &symbol_start, &symbol_end);
> > + perf_event_mmap_bpf_prog(symbol_start, symbol_end - symbol_start,
> > + buf, sizeof(buf));
> > }
>
> So perf doesn't normally issue unmap events.. We've talked about doing
> that, but so far it's never really need needed I think.
> I feels a bit weird to start issuing unmap events for this.
For reference, this surfaced here:
https://lkml.org/lkml/2017/1/27/452
Start of the thread, that involves postgresql, JIT, LLVM, perf is here:
https://lkml.org/lkml/2016/12/10/1
PeterZ provided a patch introducing PERF_RECORD_MUNMAP, went nowhere due
to having to cope with munmapping parts of existing mmaps, etc.
I'm still more in favour of introduce PERF_RECORD_MUNMAP, even if for
now it would be used just in this clean case for undoing a
PERF_RECORD_MMAP for a BPF program.
The ABI is already complicated, starting to use something called
PERF_RECORD_MMAP for unmmaping by just using a NULL name... too clever,
I think.
- Arnaldo
