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Date: Tue, 27 Nov 2012 16:59:42 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Frederic Weisbecker <fweisbec@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
Li Zhong <zhong@...ux.vnet.ibm.com>,
Gilad.Ben-Yossef.gilad@...yossef.com
Subject: Re: [PATCH] context_tracking: New context tracking susbsystem
On Tue, Nov 27, 2012 at 07:33:25PM +0100, Frederic Weisbecker wrote:
> Create a new subsystem that probes on kernel boundaries
> to keep track of the transitions between level contexts
> with two basic initial contexts: user or kernel.
>
> This is an abstraction of some RCU code that use such tracking
> to implement its userspace extended quiescent state.
>
> We need to pull this up from RCU into this new level of indirection
> because this tracking is also going to be used to implement an "on
> demand" generic virtual cputime accounting. A necessary step to
> shutdown the tick while still accounting the cputime.
I have queued this, and if it passes tests and inspection will try
pushing it for 3.8.
Thanx, Paul
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Li Zhong <zhong@...ux.vnet.ibm.com>
> Cc: Gilad Ben-Yossef gilad@...yossef.com
> ---
> Changes since last version address Gilad's comments and include ifdef fixes.
> Also CONTEXT_TRACKING_FORCE option has been moved below RCU user mode config
> as it's the only user for now.
>
> arch/Kconfig | 15 ++--
> arch/x86/Kconfig | 2 +-
> arch/x86/include/asm/{rcu.h => context_tracking.h} | 15 ++--
> arch/x86/kernel/entry_64.S | 2 +-
> arch/x86/kernel/ptrace.c | 8 +-
> arch/x86/kernel/signal.c | 5 +-
> arch/x86/kernel/traps.c | 2 +-
> arch/x86/mm/fault.c | 2 +-
> include/linux/context_tracking.h | 18 ++++
> include/linux/rcupdate.h | 2 -
> init/Kconfig | 28 ++++----
> kernel/Makefile | 1 +
> kernel/context_tracking.c | 83 ++++++++++++++++++++
> kernel/rcutree.c | 64 +---------------
> kernel/sched/core.c | 11 ++-
> 15 files changed, 150 insertions(+), 108 deletions(-)
> rename arch/x86/include/asm/{rcu.h => context_tracking.h} (63%)
> create mode 100644 include/linux/context_tracking.h
> create mode 100644 kernel/context_tracking.c
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 366ec06..cc74aae 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -300,15 +300,16 @@ config SECCOMP_FILTER
>
> See Documentation/prctl/seccomp_filter.txt for details.
>
> -config HAVE_RCU_USER_QS
> +config HAVE_CONTEXT_TRACKING
> bool
> help
> - Provide kernel entry/exit hooks necessary for userspace
> - RCU extended quiescent state. Syscalls need to be wrapped inside
> - rcu_user_exit()-rcu_user_enter() through the slow path using
> - TIF_NOHZ flag. Exceptions handlers must be wrapped as well. Irqs
> - are already protected inside rcu_irq_enter/rcu_irq_exit() but
> - preemption or signal handling on irq exit still need to be protected.
> + Provide kernel/user boundaries probes necessary for subsystems
> + that need it, such as userspace RCU extended quiescent state.
> + Syscalls need to be wrapped inside user_exit()-user_enter() through
> + the slow path using TIF_NOHZ flag. Exceptions handlers must be
> + wrapped as well. Irqs are already protected inside
> + rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
> + irq exit still need to be protected.
>
> config HAVE_VIRT_CPU_ACCOUNTING
> bool
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 46c3bff..110cfad 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -106,7 +106,7 @@ config X86
> select KTIME_SCALAR if X86_32
> select GENERIC_STRNCPY_FROM_USER
> select GENERIC_STRNLEN_USER
> - select HAVE_RCU_USER_QS if X86_64
> + select HAVE_CONTEXT_TRACKING if X86_64
> select HAVE_IRQ_TIME_ACCOUNTING
> select GENERIC_KERNEL_THREAD
> select GENERIC_KERNEL_EXECVE
> diff --git a/arch/x86/include/asm/rcu.h b/arch/x86/include/asm/context_tracking.h
> similarity index 63%
> rename from arch/x86/include/asm/rcu.h
> rename to arch/x86/include/asm/context_tracking.h
> index d1ac07a..1616562 100644
> --- a/arch/x86/include/asm/rcu.h
> +++ b/arch/x86/include/asm/context_tracking.h
> @@ -1,27 +1,26 @@
> -#ifndef _ASM_X86_RCU_H
> -#define _ASM_X86_RCU_H
> +#ifndef _ASM_X86_CONTEXT_TRACKING_H
> +#define _ASM_X86_CONTEXT_TRACKING_H
>
> #ifndef __ASSEMBLY__
> -
> -#include <linux/rcupdate.h>
> +#include <linux/context_tracking.h>
> #include <asm/ptrace.h>
>
> static inline void exception_enter(struct pt_regs *regs)
> {
> - rcu_user_exit();
> + user_exit();
> }
>
> static inline void exception_exit(struct pt_regs *regs)
> {
> -#ifdef CONFIG_RCU_USER_QS
> +#ifdef CONFIG_CONTEXT_TRACKING
> if (user_mode(regs))
> - rcu_user_enter();
> + user_enter();
> #endif
> }
>
> #else /* __ASSEMBLY__ */
>
> -#ifdef CONFIG_RCU_USER_QS
> +#ifdef CONFIG_CONTEXT_TRACKING
> # define SCHEDULE_USER call schedule_user
> #else
> # define SCHEDULE_USER call schedule
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 0c58952..98faeb3 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -56,7 +56,7 @@
> #include <asm/ftrace.h>
> #include <asm/percpu.h>
> #include <asm/asm.h>
> -#include <asm/rcu.h>
> +#include <asm/context_tracking.h>
> #include <asm/smap.h>
> #include <linux/err.h>
>
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> index eff5b8c..65b88a5 100644
> --- a/arch/x86/kernel/ptrace.c
> +++ b/arch/x86/kernel/ptrace.c
> @@ -21,7 +21,7 @@
> #include <linux/signal.h>
> #include <linux/perf_event.h>
> #include <linux/hw_breakpoint.h>
> -#include <linux/rcupdate.h>
> +#include <linux/context_tracking.h>
>
> #include <asm/uaccess.h>
> #include <asm/pgtable.h>
> @@ -1461,7 +1461,7 @@ long syscall_trace_enter(struct pt_regs *regs)
> {
> long ret = 0;
>
> - rcu_user_exit();
> + user_exit();
>
> /*
> * If we stepped into a sysenter/syscall insn, it trapped in
> @@ -1516,7 +1516,7 @@ void syscall_trace_leave(struct pt_regs *regs)
> * or do_notify_resume(), in which case we can be in RCU
> * user mode.
> */
> - rcu_user_exit();
> + user_exit();
>
> audit_syscall_exit(regs);
>
> @@ -1534,5 +1534,5 @@ void syscall_trace_leave(struct pt_regs *regs)
> if (step || test_thread_flag(TIF_SYSCALL_TRACE))
> tracehook_report_syscall_exit(regs, step);
>
> - rcu_user_enter();
> + user_enter();
> }
> diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
> index 29ad351..20ecac1 100644
> --- a/arch/x86/kernel/signal.c
> +++ b/arch/x86/kernel/signal.c
> @@ -22,6 +22,7 @@
> #include <linux/uaccess.h>
> #include <linux/user-return-notifier.h>
> #include <linux/uprobes.h>
> +#include <linux/context_tracking.h>
>
> #include <asm/processor.h>
> #include <asm/ucontext.h>
> @@ -816,7 +817,7 @@ static void do_signal(struct pt_regs *regs)
> void
> do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
> {
> - rcu_user_exit();
> + user_exit();
>
> #ifdef CONFIG_X86_MCE
> /* notify userspace of pending MCEs */
> @@ -840,7 +841,7 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
> if (thread_info_flags & _TIF_USER_RETURN_NOTIFY)
> fire_user_return_notifiers();
>
> - rcu_user_enter();
> + user_enter();
> }
>
> void signal_fault(struct pt_regs *regs, void __user *frame, char *where)
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 8276dc6..eb85866 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -55,7 +55,7 @@
> #include <asm/i387.h>
> #include <asm/fpu-internal.h>
> #include <asm/mce.h>
> -#include <asm/rcu.h>
> +#include <asm/context_tracking.h>
>
> #include <asm/mach_traps.h>
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 8e13ecb..b0b1f1d 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -18,7 +18,7 @@
> #include <asm/pgalloc.h> /* pgd_*(), ... */
> #include <asm/kmemcheck.h> /* kmemcheck_*(), ... */
> #include <asm/fixmap.h> /* VSYSCALL_START */
> -#include <asm/rcu.h> /* exception_enter(), ... */
> +#include <asm/context_tracking.h> /* exception_enter(), ... */
>
> /*
> * Page fault error code bits:
> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
> new file mode 100644
> index 0000000..e24339c
> --- /dev/null
> +++ b/include/linux/context_tracking.h
> @@ -0,0 +1,18 @@
> +#ifndef _LINUX_CONTEXT_TRACKING_H
> +#define _LINUX_CONTEXT_TRACKING_H
> +
> +#ifdef CONFIG_CONTEXT_TRACKING
> +#include <linux/sched.h>
> +
> +extern void user_enter(void);
> +extern void user_exit(void);
> +extern void context_tracking_task_switch(struct task_struct *prev,
> + struct task_struct *next);
> +#else
> +static inline void user_enter(void) { }
> +static inline void user_exit(void) { }
> +static inline void context_tracking_task_switch(struct task_struct *prev,
> + struct task_struct *next) { }
> +#endif /* !CONFIG_CONTEXT_TRACKING */
> +
> +#endif
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 8fe7c18..275aa3f 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -222,8 +222,6 @@ extern void rcu_user_enter(void);
> extern void rcu_user_exit(void);
> extern void rcu_user_enter_after_irq(void);
> extern void rcu_user_exit_after_irq(void);
> -extern void rcu_user_hooks_switch(struct task_struct *prev,
> - struct task_struct *next);
> #else
> static inline void rcu_user_enter(void) { }
> static inline void rcu_user_exit(void) { }
> diff --git a/init/Kconfig b/init/Kconfig
> index 5ac6ee0..2054e04 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -486,9 +486,13 @@ config PREEMPT_RCU
> This option enables preemptible-RCU code that is common between
> the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
>
> +config CONTEXT_TRACKING
> + bool
> +
> config RCU_USER_QS
> bool "Consider userspace as in RCU extended quiescent state"
> - depends on HAVE_RCU_USER_QS && SMP
> + depends on HAVE_CONTEXT_TRACKING && SMP
> + select CONTEXT_TRACKING
> help
> This option sets hooks on kernel / userspace boundaries and
> puts RCU in extended quiescent state when the CPU runs in
> @@ -497,24 +501,20 @@ config RCU_USER_QS
> try to keep the timer tick on for RCU.
>
> Unless you want to hack and help the development of the full
> - tickless feature, you shouldn't enable this option. It also
> + dynticks mode, you shouldn't enable this option. It also
> adds unnecessary overhead.
>
> If unsure say N
>
> -config RCU_USER_QS_FORCE
> - bool "Force userspace extended QS by default"
> - depends on RCU_USER_QS
> +config CONTEXT_TRACKING_FORCE
> + bool "Force context tracking"
> + depends on CONTEXT_TRACKING
> help
> - Set the hooks in user/kernel boundaries by default in order to
> - test this feature that treats userspace as an extended quiescent
> - state until we have a real user like a full adaptive nohz option.
> -
> - Unless you want to hack and help the development of the full
> - tickless feature, you shouldn't enable this option. It adds
> - unnecessary overhead.
> -
> - If unsure say N
> + Probe on user/kernel boundaries by default in order to
> + test the features that rely on it such as userspace RCU extended
> + quiescent states.
> + This test is there for debugging until we have a real user like the
> + full dynticks mode.
>
> config RCU_FANOUT
> int "Tree-based hierarchical RCU fanout value"
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 0dfeca4..f90bbfc 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -110,6 +110,7 @@ obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o
> obj-$(CONFIG_PADATA) += padata.o
> obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
> obj-$(CONFIG_JUMP_LABEL) += jump_label.o
> +obj-$(CONFIG_CONTEXT_TRACKING) += context_tracking.o
>
> $(obj)/configs.o: $(obj)/config_data.h
>
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> new file mode 100644
> index 0000000..e0e07fd
> --- /dev/null
> +++ b/kernel/context_tracking.c
> @@ -0,0 +1,83 @@
> +#include <linux/context_tracking.h>
> +#include <linux/rcupdate.h>
> +#include <linux/sched.h>
> +#include <linux/percpu.h>
> +#include <linux/hardirq.h>
> +
> +struct context_tracking {
> + /*
> + * When active is false, hooks are not set to
> + * minimize overhead: TIF flags are cleared
> + * and calls to user_enter/exit are ignored. This
> + * may be further optimized using static keys.
> + */
> + bool active;
> + enum {
> + IN_KERNEL = 0,
> + IN_USER,
> + } state;
> +};
> +
> +static DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
> +#ifdef CONFIG_CONTEXT_TRACKING_FORCE
> + .active = true,
> +#endif
> +};
> +
> +void user_enter(void)
> +{
> + unsigned long flags;
> +
> + /*
> + * Some contexts may involve an exception occuring in an irq,
> + * leading to that nesting:
> + * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
> + * This would mess up the dyntick_nesting count though. And rcu_irq_*()
> + * helpers are enough to protect RCU uses inside the exception. So
> + * just return immediately if we detect we are in an IRQ.
> + */
> + if (in_interrupt())
> + return;
> +
> + WARN_ON_ONCE(!current->mm);
> +
> + local_irq_save(flags);
> + if (__this_cpu_read(context_tracking.active) &&
> + __this_cpu_read(context_tracking.state) != IN_USER) {
> + __this_cpu_write(context_tracking.state, IN_USER);
> + rcu_user_enter();
> + }
> + local_irq_restore(flags);
> +}
> +
> +void user_exit(void)
> +{
> + unsigned long flags;
> +
> + /*
> + * Some contexts may involve an exception occuring in an irq,
> + * leading to that nesting:
> + * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
> + * This would mess up the dyntick_nesting count though. And rcu_irq_*()
> + * helpers are enough to protect RCU uses inside the exception. So
> + * just return immediately if we detect we are in an IRQ.
> + */
> + if (in_interrupt())
> + return;
> +
> + local_irq_save(flags);
> + if (__this_cpu_read(context_tracking.state) == IN_USER) {
> + __this_cpu_write(context_tracking.state, IN_KERNEL);
> + rcu_user_exit();
> + }
> + local_irq_restore(flags);
> +}
> +
> +void context_tracking_task_switch(struct task_struct *prev,
> + struct task_struct *next)
> +{
> + if (__this_cpu_read(context_tracking.active)) {
> + clear_tsk_thread_flag(prev, TIF_NOHZ);
> + set_tsk_thread_flag(next, TIF_NOHZ);
> + }
> +}
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 7733eb5..e441b77 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -207,9 +207,6 @@ EXPORT_SYMBOL_GPL(rcu_note_context_switch);
> DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
> .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
> .dynticks = ATOMIC_INIT(1),
> -#if defined(CONFIG_RCU_USER_QS) && !defined(CONFIG_RCU_USER_QS_FORCE)
> - .ignore_user_qs = true,
> -#endif
> };
>
> static long blimit = 10; /* Maximum callbacks per rcu_do_batch. */
> @@ -420,29 +417,7 @@ EXPORT_SYMBOL_GPL(rcu_idle_enter);
> */
> void rcu_user_enter(void)
> {
> - unsigned long flags;
> - struct rcu_dynticks *rdtp;
> -
> - /*
> - * Some contexts may involve an exception occuring in an irq,
> - * leading to that nesting:
> - * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
> - * This would mess up the dyntick_nesting count though. And rcu_irq_*()
> - * helpers are enough to protect RCU uses inside the exception. So
> - * just return immediately if we detect we are in an IRQ.
> - */
> - if (in_interrupt())
> - return;
> -
> - WARN_ON_ONCE(!current->mm);
> -
> - local_irq_save(flags);
> - rdtp = &__get_cpu_var(rcu_dynticks);
> - if (!rdtp->ignore_user_qs && !rdtp->in_user) {
> - rdtp->in_user = true;
> - rcu_eqs_enter(true);
> - }
> - local_irq_restore(flags);
> + rcu_eqs_enter(1);
> }
>
> /**
> @@ -579,27 +554,7 @@ EXPORT_SYMBOL_GPL(rcu_idle_exit);
> */
> void rcu_user_exit(void)
> {
> - unsigned long flags;
> - struct rcu_dynticks *rdtp;
> -
> - /*
> - * Some contexts may involve an exception occuring in an irq,
> - * leading to that nesting:
> - * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
> - * This would mess up the dyntick_nesting count though. And rcu_irq_*()
> - * helpers are enough to protect RCU uses inside the exception. So
> - * just return immediately if we detect we are in an IRQ.
> - */
> - if (in_interrupt())
> - return;
> -
> - local_irq_save(flags);
> - rdtp = &__get_cpu_var(rcu_dynticks);
> - if (rdtp->in_user) {
> - rdtp->in_user = false;
> - rcu_eqs_exit(true);
> - }
> - local_irq_restore(flags);
> + rcu_eqs_exit(1);
> }
>
> /**
> @@ -722,21 +677,6 @@ int rcu_is_cpu_idle(void)
> }
> EXPORT_SYMBOL(rcu_is_cpu_idle);
>
> -#ifdef CONFIG_RCU_USER_QS
> -void rcu_user_hooks_switch(struct task_struct *prev,
> - struct task_struct *next)
> -{
> - struct rcu_dynticks *rdtp;
> -
> - /* Interrupts are disabled in context switch */
> - rdtp = &__get_cpu_var(rcu_dynticks);
> - if (!rdtp->ignore_user_qs) {
> - clear_tsk_thread_flag(prev, TIF_NOHZ);
> - set_tsk_thread_flag(next, TIF_NOHZ);
> - }
> -}
> -#endif /* #ifdef CONFIG_RCU_USER_QS */
> -
> #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
>
> /*
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 36f2608..80f80df 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -72,6 +72,7 @@
> #include <linux/slab.h>
> #include <linux/init_task.h>
> #include <linux/binfmts.h>
> +#include <linux/context_tracking.h>
>
> #include <asm/switch_to.h>
> #include <asm/tlb.h>
> @@ -1886,8 +1887,8 @@ context_switch(struct rq *rq, struct task_struct *prev,
> spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
> #endif
>
> + context_tracking_task_switch(prev, next);
> /* Here we just switch the register state and the stack. */
> - rcu_user_hooks_switch(prev, next);
> switch_to(prev, next, prev);
>
> barrier();
> @@ -2911,7 +2912,7 @@ asmlinkage void __sched schedule(void)
> }
> EXPORT_SYMBOL(schedule);
>
> -#ifdef CONFIG_RCU_USER_QS
> +#ifdef CONFIG_CONTEXT_TRACKING
> asmlinkage void __sched schedule_user(void)
> {
> /*
> @@ -2920,9 +2921,9 @@ asmlinkage void __sched schedule_user(void)
> * we haven't yet exited the RCU idle mode. Do it here manually until
> * we find a better solution.
> */
> - rcu_user_exit();
> + user_exit();
> schedule();
> - rcu_user_enter();
> + user_enter();
> }
> #endif
>
> @@ -3027,7 +3028,7 @@ asmlinkage void __sched preempt_schedule_irq(void)
> /* Catch callers which need to be fixed */
> BUG_ON(ti->preempt_count || !irqs_disabled());
>
> - rcu_user_exit();
> + user_exit();
> do {
> add_preempt_count(PREEMPT_ACTIVE);
> local_irq_enable();
> --
> 1.7.5.4
>
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