Re: Question: goal of twice disabling of preemption in exception handlers

[Andy Lutomirski]

On Sun, Nov 20, 2016 at 9:52 AM, Alexnader Kuleshov
<kuleshovmail@xxxxxxxxx> wrote:
> Hello everyone,
>
> Exception handlers which may run on IST stack disable and enable preemption
> twice. For example do_int3() [1]. This one calls ist_enter() which
> disables preemption with preempt_disable() every time without any conditions.
> And later do_int3() calls preempt_disable() again [2] before do_trap().
>
> Of course we decrement preemption counter in the end of such exception
> handlers twice too. But what's actual purpose of doing this two times?
>
> [1] https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/arch/x86/kernel/traps.c?id=refs/tags/next-20161117#n530
> [2] https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/arch/x86/kernel/traps.c?id=refs/tags/next-20161117#n566
>
> Thank you.

You could submit a patch to get rid of the extra one if you like.