Re: [PATCH 08/19] context_tracking: Take NMI eqs entrypoints over RCU

["Paul E. McKenney" <paulmck@kernel.org>]

On Wed, Mar 02, 2022 at 04:47:59PM +0100, Frederic Weisbecker wrote:
> The RCU dynticks counter is going to be merged into the context tracking
> subsystem. Prepare with moving the NMI extended quiescent states
> entrypoints to context tracking. For now those are dumb redirection to
> existing RCU calls.
> 
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Acked-by: Paul E. McKenney <paulmck@kernel.org>

> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
> Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
> Cc: Joel Fernandes <joel@joelfernandes.org>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
> Cc: Yu Liao<liaoyu15@huawei.com>
> Cc: Phil Auld <pauld@redhat.com>
> Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
> Cc: Alex Belits <abelits@marvell.com>
> ---
>  Documentation/RCU/Design/Requirements/Requirements.rst |  2 +-
>  arch/Kconfig                                           |  2 +-
>  arch/arm64/kernel/entry-common.c                       |  8 ++++----
>  include/linux/context_tracking_irq.h                   |  4 ++++
>  include/linux/hardirq.h                                |  4 ++--
>  kernel/context_tracking.c                              | 10 ++++++++++
>  kernel/entry/common.c                                  |  4 ++--
>  kernel/extable.c                                       |  4 ++--
>  kernel/trace/trace.c                                   |  2 +-
>  9 files changed, 27 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
> index e3dd5d71c798..256cf260e864 100644
> --- a/Documentation/RCU/Design/Requirements/Requirements.rst
> +++ b/Documentation/RCU/Design/Requirements/Requirements.rst
> @@ -1847,7 +1847,7 @@ normal interrupts. One way that this can happen is for code that
>  directly invokes ct_irq_enter() and ct_irq_exit() to be called
>  from an NMI handler. This astonishing fact of life prompted the current
>  code structure, which has ct_irq_enter() invoking
> -rcu_nmi_enter() and ct_irq_exit() invoking rcu_nmi_exit().
> +ct_nmi_enter() and ct_irq_exit() invoking ct_nmi_exit().
>  And yes, I also learned of this requirement the hard way.
>  
>  Loadable Modules
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 66b2b6d4717b..c22b8ca0eb01 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -785,7 +785,7 @@ config HAVE_CONTEXT_TRACKING_USER_OFFSTACK
>  
>  	  - Critical entry code isn't preemptible (or better yet:
>  	    not interruptible).
> -	  - No use of RCU read side critical sections, unless rcu_nmi_enter()
> +	  - No use of RCU read side critical sections, unless ct_nmi_enter()
>  	    got called.
>  	  - No use of instrumentation, unless instrumentation_begin() got
>  	    called.
> diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
> index 43ca8cf4e1dd..6a1ea28731c8 100644
> --- a/arch/arm64/kernel/entry-common.c
> +++ b/arch/arm64/kernel/entry-common.c
> @@ -158,7 +158,7 @@ static void noinstr arm64_enter_nmi(struct pt_regs *regs)
>  	__nmi_enter();
>  	lockdep_hardirqs_off(CALLER_ADDR0);
>  	lockdep_hardirq_enter();
> -	rcu_nmi_enter();
> +	ct_nmi_enter();
>  
>  	trace_hardirqs_off_finish();
>  	ftrace_nmi_enter();
> @@ -179,7 +179,7 @@ static void noinstr arm64_exit_nmi(struct pt_regs *regs)
>  		lockdep_hardirqs_on_prepare(CALLER_ADDR0);
>  	}
>  
> -	rcu_nmi_exit();
> +	ct_nmi_exit();
>  	lockdep_hardirq_exit();
>  	if (restore)
>  		lockdep_hardirqs_on(CALLER_ADDR0);
> @@ -196,7 +196,7 @@ static void noinstr arm64_enter_el1_dbg(struct pt_regs *regs)
>  	regs->lockdep_hardirqs = lockdep_hardirqs_enabled();
>  
>  	lockdep_hardirqs_off(CALLER_ADDR0);
> -	rcu_nmi_enter();
> +	ct_nmi_enter();
>  
>  	trace_hardirqs_off_finish();
>  }
> @@ -215,7 +215,7 @@ static void noinstr arm64_exit_el1_dbg(struct pt_regs *regs)
>  		lockdep_hardirqs_on_prepare(CALLER_ADDR0);
>  	}
>  
> -	rcu_nmi_exit();
> +	ct_nmi_exit();
>  	if (restore)
>  		lockdep_hardirqs_on(CALLER_ADDR0);
>  }
> diff --git a/include/linux/context_tracking_irq.h b/include/linux/context_tracking_irq.h
> index 60e3ed15a04e..11043bf724b7 100644
> --- a/include/linux/context_tracking_irq.h
> +++ b/include/linux/context_tracking_irq.h
> @@ -7,11 +7,15 @@ void ct_irq_enter(void);
>  void ct_irq_exit(void);
>  void ct_irq_enter_irqson(void);
>  void ct_irq_exit_irqson(void);
> +void ct_nmi_enter(void);
> +void ct_nmi_exit(void);
>  #else
>  static inline void ct_irq_enter(void) { }
>  static inline void ct_irq_exit(void) { }
>  static inline void ct_irq_enter_irqson(void) { }
>  static inline void ct_irq_exit_irqson(void) { }
> +static inline void ct_nmi_enter(void) { }
> +static inline void ct_nmi_exit(void) { }
>  #endif
>  
>  #endif
> diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
> index 76878b357ffa..345cdbe9c1b7 100644
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -124,7 +124,7 @@ extern void rcu_nmi_exit(void);
>  	do {							\
>  		__nmi_enter();					\
>  		lockdep_hardirq_enter();			\
> -		rcu_nmi_enter();				\
> +		ct_nmi_enter();				\
>  		instrumentation_begin();			\
>  		ftrace_nmi_enter();				\
>  		instrumentation_end();				\
> @@ -143,7 +143,7 @@ extern void rcu_nmi_exit(void);
>  		instrumentation_begin();			\
>  		ftrace_nmi_exit();				\
>  		instrumentation_end();				\
> -		rcu_nmi_exit();					\
> +		ct_nmi_exit();					\
>  		lockdep_hardirq_exit();				\
>  		__nmi_exit();					\
>  	} while (0)
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index b63ff851472e..1686cd528966 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -267,3 +267,13 @@ void ct_irq_exit_irqson(void)
>  {
>  	rcu_irq_exit_irqson();
>  }
> +
> +noinstr void ct_nmi_enter(void)
> +{
> +	rcu_nmi_enter();
> +}
> +
> +noinstr void ct_nmi_exit(void)
> +{
> +	rcu_nmi_exit();
> +}
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index cebc98b8adc6..08230507793f 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -449,7 +449,7 @@ irqentry_state_t noinstr irqentry_nmi_enter(struct pt_regs *regs)
>  	__nmi_enter();
>  	lockdep_hardirqs_off(CALLER_ADDR0);
>  	lockdep_hardirq_enter();
> -	rcu_nmi_enter();
> +	ct_nmi_enter();
>  
>  	instrumentation_begin();
>  	trace_hardirqs_off_finish();
> @@ -469,7 +469,7 @@ void noinstr irqentry_nmi_exit(struct pt_regs *regs, irqentry_state_t irq_state)
>  	}
>  	instrumentation_end();
>  
> -	rcu_nmi_exit();
> +	ct_nmi_exit();
>  	lockdep_hardirq_exit();
>  	if (irq_state.lockdep)
>  		lockdep_hardirqs_on(CALLER_ADDR0);
> diff --git a/kernel/extable.c b/kernel/extable.c
> index b6f330f0fe74..88d4d739c5a1 100644
> --- a/kernel/extable.c
> +++ b/kernel/extable.c
> @@ -113,7 +113,7 @@ int kernel_text_address(unsigned long addr)
>  
>  	/* Treat this like an NMI as it can happen anywhere */
>  	if (no_rcu)
> -		rcu_nmi_enter();
> +		ct_nmi_enter();
>  
>  	if (is_module_text_address(addr))
>  		goto out;
> @@ -126,7 +126,7 @@ int kernel_text_address(unsigned long addr)
>  	ret = 0;
>  out:
>  	if (no_rcu)
> -		rcu_nmi_exit();
> +		ct_nmi_exit();
>  
>  	return ret;
>  }
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 7c500c708180..9434da82af8a 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3086,7 +3086,7 @@ void __trace_stack(struct trace_array *tr, unsigned int trace_ctx,
>  	}
>  
>  	/*
> -	 * When an NMI triggers, RCU is enabled via rcu_nmi_enter(),
> +	 * When an NMI triggers, RCU is enabled via ct_nmi_enter(),
>  	 * but if the above rcu_is_watching() failed, then the NMI
>  	 * triggered someplace critical, and ct_irq_enter() should
>  	 * not be called from NMI.
> -- 
> 2.25.1
>