linux-kernel - Re: [PATCH 4/7] add syscall tracepoints

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Date:	Fri, 19 Jun 2009 04:12:37 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jason Baron <jbaron@...hat.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	rostedt@...dmis.org, peterz@...radead.org,
	mathieu.desnoyers@...ymtl.ca, jiayingz@...gle.com,
	bligh@...gle.com, roland@...hat.com, fche@...hat.com
Subject: Re: [PATCH 4/7] add syscall tracepoints

On Fri, Jun 12, 2009 at 05:24:54PM -0400, Jason Baron wrote:
> 
> add two tracepoints in syscall exit and entry path, conditioned on
> TIF_SYSCALL_FTRACE. Supports the syscall trace event code.
> 
> 
> Signed-off-by: Jason Baron <jbaron@...hat.com>
> 
> ---
>  arch/x86/kernel/ptrace.c |    6 ++++--
>  include/trace/syscall.h  |   18 ++++++++++++++++++
>  kernel/tracepoint.c      |   38 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 60 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> index 09ecbde..1c7301a 100644
> --- a/arch/x86/kernel/ptrace.c
> +++ b/arch/x86/kernel/ptrace.c
> @@ -36,6 +36,8 @@
>  #include <asm/ds.h>
>  
>  #include <trace/syscall.h>
> +DEFINE_TRACE(syscall_enter);
> +DEFINE_TRACE(syscall_exit);
>  
>  #include "tls.h"
>  
> @@ -1498,7 +1500,7 @@ asmregparm long syscall_trace_enter(struct pt_regs *regs)
>  		ret = -1L;
>  
>  	if (unlikely(test_thread_flag(TIF_SYSCALL_FTRACE)))
> -		ftrace_syscall_enter(regs);
> +		trace_syscall_enter(regs, regs->orig_ax);
>  
>  	if (unlikely(current->audit_context)) {
>  		if (IS_IA32)
> @@ -1524,7 +1526,7 @@ asmregparm void syscall_trace_leave(struct pt_regs *regs)
>  		audit_syscall_exit(AUDITSC_RESULT(regs->ax), regs->ax);
>  
>  	if (unlikely(test_thread_flag(TIF_SYSCALL_FTRACE)))
> -		ftrace_syscall_exit(regs);
> +		trace_syscall_exit(regs, regs->ax);
>  
>  	if (test_thread_flag(TIF_SYSCALL_TRACE))
>  		tracehook_report_syscall_exit(regs, 0);
> diff --git a/include/trace/syscall.h b/include/trace/syscall.h
> index 8cfe515..d5d8310 100644
> --- a/include/trace/syscall.h
> +++ b/include/trace/syscall.h
> @@ -2,6 +2,24 @@
>  #define _TRACE_SYSCALL_H
>  
>  #include <asm/ptrace.h>
> +#include <linux/tracepoint.h>
> +
> +extern void syscall_regfunc(void);
> +extern void syscall_unregfunc(void);
> +
> +DECLARE_TRACE_REG(syscall_enter,
> +	TP_PROTO(struct pt_regs *regs, long id),
> +	TP_ARGS(regs, id),
> +	syscall_regfunc,
> +	syscall_unregfunc
> +);
> +
> +DECLARE_TRACE_REG(syscall_exit,
> +	TP_PROTO(struct pt_regs *regs, long ret),
> +	TP_ARGS(regs, ret),
> +	syscall_regfunc,
> +	syscall_unregfunc
> +);
>  
>  /*
>   * A syscall entry in the ftrace syscalls array.
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 1ef5d3a..5b34ff9 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c



At a first glance I wasn't sure tracepoint.c is the right
place for these.
But indeed putting those two callbacks here avoids any
dependency to the syscall tracer when someone else needs
the syscall tracepoints.

Well, I guess we can keep them there.



> @@ -24,6 +24,7 @@
>  #include <linux/tracepoint.h>
>  #include <linux/err.h>
>  #include <linux/slab.h>
> +#include <linux/sched.h>
>  
>  extern struct tracepoint __start___tracepoints[];
>  extern struct tracepoint __stop___tracepoints[];
> @@ -577,3 +578,40 @@ static int init_tracepoints(void)
>  __initcall(init_tracepoints);
>  
>  #endif /* CONFIG_MODULES */
> +
> +DEFINE_MUTEX(regfunc_mutex);
> +int sys_tracepoint_refcount;


Looks like regfunc_mutex is only there to protect
sys_tracepoint_refcount. May be you can just make it atomic_t?

Thanks,
Frederic.


> +
> +void syscall_regfunc(void)
> +{
> +	unsigned long flags;
> +	struct task_struct *g, *t;
> +
> +	mutex_lock(&regfunc_mutex);
> +	if (!sys_tracepoint_refcount) {
> +		read_lock_irqsave(&tasklist_lock, flags);
> +		do_each_thread(g, t) {
> +			set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
> +		} while_each_thread(g, t);
> +		read_unlock_irqrestore(&tasklist_lock, flags);
> +	}
> +	sys_tracepoint_refcount++;
> +	mutex_unlock(&regfunc_mutex);
> +}
> +
> +void syscall_unregfunc(void)
> +{
> +	unsigned long flags;
> +	struct task_struct *g, *t;
> +
> +	mutex_lock(&regfunc_mutex);
> +	sys_tracepoint_refcount--;
> +	if (!sys_tracepoint_refcount) {
> +		read_lock_irqsave(&tasklist_lock, flags);
> +		do_each_thread(g, t) {
> +			clear_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
> +		} while_each_thread(g, t);
> +		read_unlock_irqrestore(&tasklist_lock, flags);
> +	}
> +	mutex_unlock(&regfunc_mutex);
> +}
> -- 
> 1.6.0.6
> 

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