linux-kernel - Re: [PATCH] rcu: Fixup noinstr warnings

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Date:   Wed, 3 Jun 2020 02:59:32 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Marco Elver <elver@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Will Deacon <will@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rcu: Fixup noinstr warnings

On Wed, Jun 03, 2020 at 10:48:18AM +0200, Peter Zijlstra wrote:
> On Tue, Jun 02, 2020 at 09:38:53PM +0200, Peter Zijlstra wrote:
> 
> > That said; noinstr's __no_sanitize combined with atomic_t might be
> > 'interesting', because the regular atomic things have explicit
> > annotations in them. That should give validation warnings for the right
> > .config, I'll have to go try -- so far I've made sure to never enable
> > the *SAN stuff.
> 
> ---
> Subject: rcu: Fixup noinstr warnings
> 
> A KCSAN build revealed we have explicit annoations through atomic_t
> usage, switch to arch_atomic_*() for the respective functions.
> 
> vmlinux.o: warning: objtool: rcu_nmi_exit()+0x4d: call to __kcsan_check_access() leaves .noinstr.text section
> vmlinux.o: warning: objtool: rcu_dynticks_eqs_enter()+0x25: call to __kcsan_check_access() leaves .noinstr.text section
> vmlinux.o: warning: objtool: rcu_nmi_enter()+0x4f: call to __kcsan_check_access() leaves .noinstr.text section
> vmlinux.o: warning: objtool: rcu_dynticks_eqs_exit()+0x2a: call to __kcsan_check_access() leaves .noinstr.text section
> vmlinux.o: warning: objtool: __rcu_is_watching()+0x25: call to __kcsan_check_access() leaves .noinstr.text section
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

This one does not apply cleanly onto the -rcu tree's "dev" branch, so
I am guessing that it is intended to be carried in -tip with yours and
Thomas's patch series.

If you do instead want this in -rcu, please let me know.

							Thanx, Paul

> ---
>  kernel/rcu/tree.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index c716eadc7617..162656b80db9 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -250,7 +250,7 @@ static noinstr void rcu_dynticks_eqs_enter(void)
>  	 * next idle sojourn.
>  	 */
>  	rcu_dynticks_task_trace_enter();  // Before ->dynticks update!
> -	seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
> +	seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
>  	// RCU is no longer watching.  Better be in extended quiescent state!
>  	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
>  		     (seq & RCU_DYNTICK_CTRL_CTR));
> @@ -274,13 +274,13 @@ static noinstr void rcu_dynticks_eqs_exit(void)
>  	 * and we also must force ordering with the next RCU read-side
>  	 * critical section.
>  	 */
> -	seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
> +	seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
>  	// RCU is now watching.  Better not be in an extended quiescent state!
>  	rcu_dynticks_task_trace_exit();  // After ->dynticks update!
>  	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
>  		     !(seq & RCU_DYNTICK_CTRL_CTR));
>  	if (seq & RCU_DYNTICK_CTRL_MASK) {
> -		atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
> +		arch_atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
>  		smp_mb__after_atomic(); /* _exit after clearing mask. */
>  	}
>  }
> @@ -313,7 +313,7 @@ static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void)
>  {
>  	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
>  
> -	return !(atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
> +	return !(arch_atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
>  }
>  
>  /*
> @@ -692,6 +692,7 @@ noinstr void rcu_nmi_exit(void)
>  {
>  	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
>  
> +	instrumentation_begin();
>  	/*
>  	 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
>  	 * (We are exiting an NMI handler, so RCU better be paying attention
> @@ -705,7 +706,6 @@ noinstr void rcu_nmi_exit(void)
>  	 * leave it in non-RCU-idle state.
>  	 */
>  	if (rdp->dynticks_nmi_nesting != 1) {
> -		instrumentation_begin();
>  		trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2,
>  				  atomic_read(&rdp->dynticks));
>  		WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
> @@ -714,7 +714,6 @@ noinstr void rcu_nmi_exit(void)
>  		return;
>  	}
>  
> -	instrumentation_begin();
>  	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
>  	trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
>  	WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */