linux-kernel - Re: [RFC patch 10/15] x86/entry: Move irq tracing to C code

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Date:   Mon, 23 Sep 2019 10:47:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [RFC patch 10/15] x86/entry: Move irq tracing to C code

On Thu, Sep 19, 2019 at 05:03:24PM +0200, Thomas Gleixner wrote:
> To prepare for converting the exit to usermode code to the generic version,
> move the irqflags tracing into C code.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/entry/common.c          |   10 ++++++++++
>  arch/x86/entry/entry_32.S        |   11 +----------
>  arch/x86/entry/entry_64.S        |   10 ++--------
>  arch/x86/entry/entry_64_compat.S |   21 ---------------------
>  4 files changed, 13 insertions(+), 39 deletions(-)
> 
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -102,6 +102,8 @@ static void exit_to_usermode_loop(struct
>  	struct thread_info *ti = current_thread_info();
>  	u32 cached_flags;
>  
> +	trace_hardirqs_off();

Bah.. so this gets called from:

 - C code, with IRQs disabled
 - entry_64.S:error_exit
 - entry_32.S:resume_userspace

The first obviously doesn't need this annotation, but this patch doesn't
remove the TRACE_IRQS_OFF from entry_64.S and only the 32bit case is
changed.

Is that entry_64.S case an oversight, or do we need an extensive comment
on this one?

>  	addr_limit_user_check();
>  
>  	lockdep_assert_irqs_disabled();
> @@ -137,6 +139,8 @@ static void exit_to_usermode_loop(struct
>  	user_enter_irqoff();
>  
>  	mds_user_clear_cpu_buffers();
> +

	/* Return to userspace (IRET) will re-enable interrupts */
> +	trace_hardirqs_on();
>  }