Re: [PATCH 1/5] context_tracking: generalize context tracking APIs to support user and guest

Paul E. McKenney
2015-02-10T21:28:32Z

On Tue, Feb 10, 2015 at 03:27:50PM -0500, riel@redhat.com wrote:
> From: Rik van Riel <riel@redhat.com>
>
> Split out the mechanism from context_tracking_user_enter and
> context_tracking_user_exit into context_tracking_enter and
> context_tracking_exit. Leave the old functions in order to avoid
> breaking ARM, which calls these functions from assembler code,
> and cannot easily use C enum parameters.
>
> Add the expected ctx_state as a parameter to context_tracking_enter and
> context_tracking_exit, allowing the same functions to not just track
> kernel <> user space switching, but also kernel <> guest transitions.
>
> Signed-off-by: Rik van Riel <riel@redhat.com>

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
> include/linux/context_tracking.h | 8 +++++---
> kernel/context_tracking.c | 43 ++++++++++++++++++++++++++--------------
> 2 files changed, 33 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
> index 37b81bd51ec0..954253283709 100644
> --- a/include/linux/context_tracking.h
> +++ b/include/linux/context_tracking.h
> @@ -10,6 +10,8 @@
> #ifdef CONFIG_CONTEXT_TRACKING
> extern void context_tracking_cpu_set(int cpu);
>
> +extern void context_tracking_enter(enum ctx_state state);
> +extern void context_tracking_exit(enum ctx_state state);
> extern void context_tracking_user_enter(void);
> extern void context_tracking_user_exit(void);
> extern void __context_tracking_task_switch(struct task_struct *prev,
> @@ -35,7 +37,7 @@ static inline enum ctx_state exception_enter(void)
> return 0;
>
> prev_ctx = this_cpu_read(context_tracking.state);
> - context_tracking_user_exit();
> + context_tracking_exit(prev_ctx);
>
> return prev_ctx;
> }
> @@ -43,8 +45,8 @@ static inline enum ctx_state exception_enter(void)
> static inline void exception_exit(enum ctx_state prev_ctx)
> {
> if (context_tracking_is_enabled()) {
> - if (prev_ctx == IN_USER)
> - context_tracking_user_enter();
> + if (prev_ctx != IN_KERNEL)
> + context_tracking_enter(prev_ctx);
> }
> }
>
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 937ecdfdf258..38e38aeac8b9 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -39,15 +39,15 @@ void context_tracking_cpu_set(int cpu)
> }
>
> /**
> - * context_tracking_user_enter - Inform the context tracking that the CPU is going to
> - * enter userspace mode.
> + * context_tracking_enter - Inform the context tracking that the CPU is going
> + * enter user or guest space mode.
> *
> * This function must be called right before we switch from the kernel
> - * to userspace, when it's guaranteed the remaining kernel instructions
> - * to execute won't use any RCU read side critical section because this
> - * function sets RCU in extended quiescent state.
> + * to user or guest space, when it's guaranteed the remaining kernel
> + * instructions to execute won't use any RCU read side critical section
> + * because this function sets RCU in extended quiescent state.
> */
> -void context_tracking_user_enter(void)
> +void context_tracking_enter(enum ctx_state state)
> {
> unsigned long flags;
>
> @@ -75,7 +75,7 @@ void context_tracking_user_enter(void)
> WARN_ON_ONCE(!current->mm);
>
> local_irq_save(flags);
> - if ( __this_cpu_read(context_tracking.state) != IN_USER) {
> + if ( __this_cpu_read(context_tracking.state) != state) {
> if (__this_cpu_read(context_tracking.active)) {
> trace_user_enter(0);
> /*
> @@ -101,24 +101,31 @@ void context_tracking_user_enter(void)
> * OTOH we can spare the calls to vtime and RCU when context_tracking.active
> * is false because we know that CPU is not tickless.
> */
> - __this_cpu_write(context_tracking.state, IN_USER);
> + __this_cpu_write(context_tracking.state, state);
> }
> local_irq_restore(flags);
> }
> +NOKPROBE_SYMBOL(context_tracking_enter);
> +
> +void context_tracking_user_enter(void)
> +{
> + context_tracking_enter(IN_USER);
> +}
> NOKPROBE_SYMBOL(context_tracking_user_enter);
>
> /**
> - * context_tracking_user_exit - Inform the context tracking that the CPU is
> - * exiting userspace mode and entering the kernel.
> + * context_tracking_exit - Inform the context tracking that the CPU is
> + * exiting user or guest mode and entering the kernel.
> *
> - * This function must be called after we entered the kernel from userspace
> - * before any use of RCU read side critical section. This potentially include
> - * any high level kernel code like syscalls, exceptions, signal handling, etc...
> + * This function must be called after we entered the kernel from user or
> + * guest space before any use of RCU read side critical section. This
> + * potentially include any high level kernel code like syscalls, exceptions,
> + * signal handling, etc...
> *
> * This call supports re-entrancy. This way it can be called from any exception
> * handler without needing to know if we came from userspace or not.
> */
> -void context_tracking_user_exit(void)
> +void context_tracking_exit(enum ctx_state state)
> {
> unsigned long flags;
>
> @@ -129,7 +136,7 @@ void context_tracking_user_exit(void)
> return;
>
> local_irq_save(flags);
> - if (__this_cpu_read(context_tracking.state) == IN_USER) {
> + if (__this_cpu_read(context_tracking.state) == state) {
> if (__this_cpu_read(context_tracking.active)) {
> /*
> * We are going to run code that may use RCU. Inform
> @@ -143,6 +150,12 @@ void context_tracking_user_exit(void)
> }
> local_irq_restore(flags);
> }
> +NOKPROBE_SYMBOL(context_tracking_exit);
> +
> +void context_tracking_user_exit(void)
> +{
> + context_tracking_exit(IN_USER);
> +}
> NOKPROBE_SYMBOL(context_tracking_user_exit);
>
> /**
> --
> 1.9.3
>