linux-kernel - Re: [PATCH 2/6] trace syscalls: Remove redundant syscall

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Date:	Tue, 07 Dec 2010 09:54:42 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ian Munsie <imunsie@....ibm.com>
Cc:	Avantika Mathur <mathur@...ux.vnet.ibm.com>,
	Jason Baron <jbaron@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] trace syscalls: Remove redundant syscall_nr checks

On Tue, 2010-12-07 at 15:29 +1100, Ian Munsie wrote:
> From: Ian Munsie <imunsie@....ibm.com>
> 
> With the ftrace events now checking if the syscall_nr is valid upon
> initialisation, there is no need to verify it when registering and
> unregistering the events, so remove the check.

I still like to keep these checks. I don't mind redundant checks that
are in slow paths, as they may catch a bug on a change in the future.

What you could do is change these to:

	if (WARN_ON_ONCE(num < 0 || num >= NR_syscalls))

-- Steve

> 
> Signed-off-by: Ian Munsie <imunsie@....ibm.com>
> ---
>  kernel/trace/trace_syscalls.c |    9 +--------
>  1 files changed, 1 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index 14f4c02..5e34b49 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -367,8 +367,6 @@ int reg_event_syscall_enter(struct ftrace_event_call *call)
>  	int num;
>  
>  	num = ((struct syscall_metadata *)call->data)->syscall_nr;
> -	if (num < 0 || num >= NR_syscalls)
> -		return -ENOSYS;
>  	mutex_lock(&syscall_trace_lock);
>  	if (!sys_refcount_enter)
>  		ret = register_trace_sys_enter(ftrace_syscall_enter, NULL);
> @@ -385,8 +383,6 @@ void unreg_event_syscall_enter(struct ftrace_event_call *call)
>  	int num;
>  
>  	num = ((struct syscall_metadata *)call->data)->syscall_nr;
> -	if (num < 0 || num >= NR_syscalls)
> -		return;
>  	mutex_lock(&syscall_trace_lock);
>  	sys_refcount_enter--;
>  	clear_bit(num, enabled_enter_syscalls);
> @@ -401,8 +397,7 @@ int reg_event_syscall_exit(struct ftrace_event_call *call)
>  	int num;
>  
>  	num = ((struct syscall_metadata *)call->data)->syscall_nr;
> -	if (num < 0 || num >= NR_syscalls)
> -		return -ENOSYS;
> +
>  	mutex_lock(&syscall_trace_lock);
>  	if (!sys_refcount_exit)
>  		ret = register_trace_sys_exit(ftrace_syscall_exit, NULL);
> @@ -419,8 +414,6 @@ void unreg_event_syscall_exit(struct ftrace_event_call *call)
>  	int num;
>  
>  	num = ((struct syscall_metadata *)call->data)->syscall_nr;
> -	if (num < 0 || num >= NR_syscalls)
> -		return;
>  	mutex_lock(&syscall_trace_lock);
>  	sys_refcount_exit--;
>  	clear_bit(num, enabled_exit_syscalls);


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