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

From: Paul E. McKenney
Date: Thu Mar 10 2022 - 14:47:58 EST

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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@xxxxxxxxxx>

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

> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx>
> Cc: Uladzislau Rezki <uladzislau.rezki@xxxxxxxx>
> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> Cc: Nicolas Saenz Julienne <nsaenz@xxxxxxxxxx>
> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
> Cc: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
> Cc: Yu Liao<liaoyu15@xxxxxxxxxx>
> Cc: Phil Auld <pauld@xxxxxxxxxx>
> Cc: Paul Gortmaker<paul.gortmaker@xxxxxxxxxxxxx>
> Cc: Alex Belits <abelits@xxxxxxxxxxx>
> ---
> 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
>

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