linux-kernel - Re: [PATCH 16/43] x86/irq: Remove an old outdated comment about context tracking races

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Message-ID: <20171125120505.e66dr3zr5nhv4ehy@pd.tnic>
Date:   Sat, 25 Nov 2017 13:05:05 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 16/43] x86/irq: Remove an old outdated comment about
 context tracking races

On Fri, Nov 24, 2017 at 06:23:44PM +0100, Ingo Molnar wrote:
> From: Andy Lutomirski <luto@...nel.org>
> 
> That race has been fixed and code cleaned up for a while now.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Borislav Petkov <bpetkov@...e.de>
> Cc: Brian Gerst <brgerst@...il.com>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Link: https://lkml.kernel.org/r/12e75976dbbb7ece2b0a64238f1d3892dfed1e16.1511497875.git.luto@kernel.org
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---
>  arch/x86/kernel/irq.c | 12 ------------
>  1 file changed, 12 deletions(-)
> 
> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
> index 49cfd9fe7589..68e1867cca80 100644
> --- a/arch/x86/kernel/irq.c
> +++ b/arch/x86/kernel/irq.c
> @@ -219,18 +219,6 @@ __visible unsigned int __irq_entry do_IRQ(struct pt_regs *regs)
>  	/* high bit used in ret_from_ code  */
>  	unsigned vector = ~regs->orig_ax;
>  
> -	/*
> -	 * NB: Unlike exception entries, IRQ entries do not reliably
> -	 * handle context tracking in the low-level entry code.  This is
> -	 * because syscall entries execute briefly with IRQs on before
> -	 * updating context tracking state, so we can take an IRQ from
> -	 * kernel mode with CONTEXT_USER.  The low-level entry code only
> -	 * updates the context if we came from user mode, so we won't
> -	 * switch to CONTEXT_KERNEL.  We'll fix that once the syscall
> -	 * code is cleaned up enough that we can cleanly defer enabling
> -	 * IRQs.
> -	 */
> -
>  	entering_irq();
>  
>  	/* entering_irq() tells RCU that we're not quiescent.  Check it. */
> -- 

Reviewed-by: Borislav Petkov <bp@...e.de>

Also, fixes like that should move to the top of the patchset.

-- 
Regards/Gruss,
    Boris.

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