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

Josh Triplett
2012-08-31T23:59:21Z

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
>