Re: [PATCH tip/core/rcu 08/26] x86: Syscall hooks for userspace RCU extended QS

[Josh Triplett <josh@joshtriplett.org>]

On Thu, Aug 30, 2012 at 02:05:25PM -0700, Paul E. McKenney wrote:
> From: Frederic Weisbecker <fweisbec@gmail.com>
> 
> Add syscall slow path hooks to notify syscall entry
> and exit on CPUs that want to support userspace RCU
> extended quiescent state.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Alessio Igor Bogani <abogani@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Avi Kivity <avi@redhat.com>
> Cc: Chris Metcalf <cmetcalf@tilera.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Geoff Levand <geoff@infradead.org>
> Cc: Gilad Ben Yossef <gilad@benyossef.com>
> Cc: Hakan Akkan <hakanakkan@gmail.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Kevin Hilman <khilman@ti.com>
> Cc: Max Krasnyansky <maxk@qualcomm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Stephen Hemminger <shemminger@vyatta.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

This seems reasonable; presumably you plan to add something actually
setting TIF_NOHZ in a subsequent patch series?

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

>  arch/x86/include/asm/thread_info.h |   10 +++++++---
>  arch/x86/kernel/ptrace.c           |    5 +++++
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
> index 89f794f..c535d84 100644
> --- a/arch/x86/include/asm/thread_info.h
> +++ b/arch/x86/include/asm/thread_info.h
> @@ -89,6 +89,7 @@ struct thread_info {
>  #define TIF_NOTSC		16	/* TSC is not accessible in userland */
>  #define TIF_IA32		17	/* IA32 compatibility process */
>  #define TIF_FORK		18	/* ret_from_fork */
> +#define TIF_NOHZ		19	/* in adaptive nohz mode */
>  #define TIF_MEMDIE		20	/* is terminating due to OOM killer */
>  #define TIF_DEBUG		21	/* uses debug registers */
>  #define TIF_IO_BITMAP		22	/* uses I/O bitmap */
> @@ -114,6 +115,7 @@ struct thread_info {
>  #define _TIF_NOTSC		(1 << TIF_NOTSC)
>  #define _TIF_IA32		(1 << TIF_IA32)
>  #define _TIF_FORK		(1 << TIF_FORK)
> +#define _TIF_NOHZ		(1 << TIF_NOHZ)
>  #define _TIF_DEBUG		(1 << TIF_DEBUG)
>  #define _TIF_IO_BITMAP		(1 << TIF_IO_BITMAP)
>  #define _TIF_FORCED_TF		(1 << TIF_FORCED_TF)
> @@ -126,12 +128,13 @@ struct thread_info {
>  /* work to do in syscall_trace_enter() */
>  #define _TIF_WORK_SYSCALL_ENTRY	\
>  	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | _TIF_SYSCALL_AUDIT |	\
> -	 _TIF_SECCOMP | _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
> +	 _TIF_SECCOMP | _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT |	\
> +	 _TIF_NOHZ)
>  
>  /* work to do in syscall_trace_leave() */
>  #define _TIF_WORK_SYSCALL_EXIT	\
>  	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SINGLESTEP |	\
> -	 _TIF_SYSCALL_TRACEPOINT)
> +	 _TIF_SYSCALL_TRACEPOINT | _TIF_NOHZ)
>  
>  /* work to do on interrupt/exception return */
>  #define _TIF_WORK_MASK							\
> @@ -141,7 +144,8 @@ struct thread_info {
>  
>  /* work to do on any return to user space */
>  #define _TIF_ALLWORK_MASK						\
> -	((0x0000FFFF & ~_TIF_SECCOMP) | _TIF_SYSCALL_TRACEPOINT)
> +	((0x0000FFFF & ~_TIF_SECCOMP) | _TIF_SYSCALL_TRACEPOINT |	\
> +	_TIF_NOHZ)
>  
>  /* Only used for 64 bit */
>  #define _TIF_DO_NOTIFY_MASK						\
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> index c4c6a5c..9f94f8e 100644
> --- a/arch/x86/kernel/ptrace.c
> +++ b/arch/x86/kernel/ptrace.c
> @@ -21,6 +21,7 @@
>  #include <linux/signal.h>
>  #include <linux/perf_event.h>
>  #include <linux/hw_breakpoint.h>
> +#include <linux/rcupdate.h>
>  
>  #include <asm/uaccess.h>
>  #include <asm/pgtable.h>
> @@ -1463,6 +1464,8 @@ long syscall_trace_enter(struct pt_regs *regs)
>  {
>  	long ret = 0;
>  
> +	rcu_user_exit();
> +
>  	/*
>  	 * If we stepped into a sysenter/syscall insn, it trapped in
>  	 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
> @@ -1526,4 +1529,6 @@ void syscall_trace_leave(struct pt_regs *regs)
>  			!test_thread_flag(TIF_SYSCALL_EMU);
>  	if (step || test_thread_flag(TIF_SYSCALL_TRACE))
>  		tracehook_report_syscall_exit(regs, step);
> +
> +	rcu_user_enter();
>  }
> -- 
> 1.7.8
>