Re: [PATCH v3 0/6] Static calls

[Linus Torvalds]

On Fri, Jan 11, 2019 at 11:24 AM <hpa@xxxxxxxxx> wrote:
>
> I still don't see why can't simply spin in the #BP handler until the patch is complete.

So here's at least one problem:

text_poke_bp()
  text_poke(addr, &int3, sizeof(int3));
   *interrupt*
      interrupt has a static call
        *BP*
          poke_int3_handler
             *BOOM*

Note how at BOOM we cannot just spin (or return) to wait for the
'int3' to be switched back. Becuase it never will. Because we are
interrupting the thing that would do that switch-back.

So we'd have to do the 'text_poke_bp()' sequence with interrupts
disabled. Which we can't do right now at least, because part of that
sequence involves that on_each_cpu(do_sync_core) thing, which needs
interrupts enabled.

See?

Or am I missing something?

            Linus