linux-kernel - Re: [REGRESSION] x86/entry: TIF_SINGLESTEP handling is still broken

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Message-ID: <87mtwozwn3.fsf@collabora.com>
Date:   Sun, 31 Jan 2021 15:20:16 -0500
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Yuxuan Shui <yshuiv7@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "Robert O'Callahan" <rocallahan@...il.com>,
        Kyle Huey <me@...ehuey.com>
Subject: Re: [REGRESSION] x86/entry: TIF_SINGLESTEP handling is still broken

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Sun, Jan 31, 2021 at 10:54 AM Yuxuan Shui <yshuiv7@...il.com> wrote:
>>
>> But renaming the definition in x86 is not enough, as TIF_SINGLESTEP is
>> set in current_thread_info()->flags, and the same commit has removed the
>> code that checks those flags. We have to also migrate TIF_SINGLESTEP from
>> thread info flags to syscall work flags, to make the whole thing work again.
>
> Ok, so I now have the first fix merged, but what's the next step here?
>
> As you say, the x86 ARCH_SYSCALL_EXIT_WORK is now entirely unused.
>
> It's called ARCH_SYSCALL_WORK_EXIT these days, but that's for the
> SYSCALL_WORK_SYSCALL_xyz flags, not for the TIF_xyz ones.
>
> Revert? Or does somebody have a fix patch?

I think we should migrate TIF_SINGLESTEP to a SYSCALL_WORK flag as that
is just a simple refactor. I can get a patch to you and Thomas during
the first part of the week, for the next -rc. I will also review the x86
version of ARCH_SYSCALL_EXIT WORK to make sure i didn't miss anything
else.

Reverting would be slightly be annoying as it requires reverting syscall
user dispatch as well.

-- 
Gabriel Krisman Bertazi