From 91d1aa43d30505b0b825db8898ffc80a8eca96c7 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 27 Nov 2012 19:33:25 +0100 Subject: [PATCH] context_tracking: New context tracking susbsystem 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. Signed-off-by: Frederic Weisbecker Cc: Andrew Morton Cc: H. Peter Anvin Cc: Ingo Molnar Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Li Zhong Cc: Gilad Ben-Yossef Reviewed-by: Steven Rostedt [ paulmck: fix whitespace error and email address. ] Signed-off-by: Paul E. McKenney --- arch/Kconfig | 15 ++-- arch/x86/Kconfig | 2 +- .../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 366ec06a5185..cc74aaea116c 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 46c3bff3ced2..110cfad24f26 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 d1ac07a23979..1616562683e9 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 +#include #include 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 0c58952d64e8..98faeb30139d 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -56,7 +56,7 @@ #include #include #include -#include +#include #include #include diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index eff5b8c68652..65b88a5dc1a8 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -21,7 +21,7 @@ #include #include #include -#include +#include #include #include @@ -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 29ad351804e9..20ecac112e74 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include @@ -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 8276dc6794cc..eb8586693e0b 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -55,7 +55,7 @@ #include #include #include -#include +#include #include diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 8e13ecb41bee..7a529cbab7ad 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -18,7 +18,7 @@ #include /* pgd_*(), ... */ #include /* kmemcheck_*(), ... */ #include /* VSYSCALL_START */ -#include /* exception_enter(), ... */ +#include /* 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 000000000000..e24339ccb7f0 --- /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 + +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 8fe7c1840d30..275aa3f1062d 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 5ac6ee094225..2054e048bb98 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 0dfeca4324ee..f90bbfc9727f 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 000000000000..e0e07fd55508 --- /dev/null +++ b/kernel/context_tracking.c @@ -0,0 +1,83 @@ +#include +#include +#include +#include +#include + +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 7733eb56e156..e441b77b614e 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 36f260864f65..80f80dfca70e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -72,6 +72,7 @@ #include #include #include +#include #include #include @@ -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(); -- 2.39.5