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 <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Gilad Ben-Yossef <gilad@benyossef.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
[ paulmck: fix whitespace error and email address. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 8 insertions, 7 deletions

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