linux-kernel - Re: [PATCH] x86/entry: Fix noinstr warning in __enter_from_user

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Message-ID: <87jzzaa2uq.ffs@tglx>
Date:   Tue, 21 Mar 2023 10:08:29 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/entry: Fix noinstr warning in __enter_from_user_mode()

On Sat, Feb 25 2023 at 16:01, Josh Poimboeuf wrote:
> __enter_from_user_mode() is triggering noinstr warnings with
> CONFIG_DEBUG_PREEMPT due to its call of preempt_count_add() via
> ct_state().
>
> The preemption disable isn't needed as interrupts are already disabled.
> And the context_tracking_enabled() check in ct_state() also isn't needed
> as that's already being done by the CT_WARN_ON().
>
> Just use __ct_state() instead.
>
> Fixes the following warnings:
>
>   vmlinux.o: warning: objtool: enter_from_user_mode+0xba: call to preempt_count_add() leaves .noinstr.text section
>   vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0xf9: call to preempt_count_add() leaves .noinstr.text section
>   vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0xc7: call to preempt_count_add() leaves .noinstr.text section
>   vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0xba: call to preempt_count_add() leaves .noinstr.text section
>
> Fixes: 171476775d32 ("context_tracking: Convert state to atomic_t")
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
>  include/linux/context_tracking.h | 1 +
>  kernel/entry/common.c            | 2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
> index d4afa8508a80..3a7909ed5498 100644
> --- a/include/linux/context_tracking.h
> +++ b/include/linux/context_tracking.h
> @@ -96,6 +96,7 @@ static inline void user_exit_irqoff(void) { }
>  static inline int exception_enter(void) { return 0; }
>  static inline void exception_exit(enum ctx_state prev_ctx) { }
>  static inline int ct_state(void) { return -1; }
> +static inline int __ct_state(void) { return -1; }

This results in a redefinition warning due to CONFIG_CONTEXT_TRACKING=y
and CONFIG_CONFIG_TRACKING_USER=n.

Those headers are a fricking mess.

Thanks,

        tglx