Re: [PATCH v3 0/6] Static calls

[hpa]

On January 11, 2019 11:34:34 AM PST, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>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

Ok, I was thinking far more about spinning with an IRET and letting the exception be delivered. Patching with interrupts disabled have other problems... 
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