# Re: \[PATCH v6 1/9\] kernel: Support TIF\_SYSCALL\_INTERCEPT flag

- List: linux-api
- 2 messages, 2 authors
- Page: https://ratatoskr.run/linux-api/2020/09/6102575/t

## Re: \[PATCH v6 1/9\] kernel: Support TIF\_SYSCALL\_INTERCEPT flag

- From: Gabriel Krisman Bertazi \<hidden\>
- Date: 2020-09-11 20:08:58 
- Message: https://ratatoskr.run/linux-api/2020/09/6102575.md

```text
peterz@infradead.org writes:

> On Fri, Sep 04, 2020 at 04:31:39PM -0400, Gabriel Krisman Bertazi wrote:
>> +static inline void __set_tsk_syscall_intercept(struct task_struct *tsk,
>> +					   unsigned int type)
>> +{
>> +	tsk->syscall_intercept |= type;
>> +
>> +	if (tsk->syscall_intercept)
>> +		set_tsk_thread_flag(tsk, TIF_SYSCALL_INTERCEPT);
>> +}
>
> Did the above want to be:
>
> 	unsigned int old = tsk->syscall_intercept;
> 	tsk->syscall_intercept |= type;
> 	if (!old)
> 		set_tsk_thread_flag(tsk, TIF_SYSCALL_INTERCEPT)
>

Hi Peter,

Thanks for the review!

I'm not sure this change gains us anything.  For now,
__set_tsk_syscall_intercept cannot be called with !type, so both
versions behave the same, but my version is safe with that scenario.
This won't be called frequent enough for the extra calls to
set_tsk_thread_flag matter.  Am I missing something?

Thanks,

-- 
Gabriel Krisman Bertazi
```

## Re: \[PATCH v6 1/9\] kernel: Support TIF\_SYSCALL\_INTERCEPT flag

- From: Peter Zijlstra \<peterz@infradead.org\>
- Date: 2020-09-24 11:24:47 
- Message: https://ratatoskr.run/linux-api/2020/09/6117700.md

```text
On Fri, Sep 11, 2020 at 04:08:45PM -0400, Gabriel Krisman Bertazi wrote:
> peterz@infradead.org writes:
> 
> > On Fri, Sep 04, 2020 at 04:31:39PM -0400, Gabriel Krisman Bertazi wrote:
> >> +static inline void __set_tsk_syscall_intercept(struct task_struct *tsk,
> >> +					   unsigned int type)
> >> +{
> >> +	tsk->syscall_intercept |= type;
> >> +
> >> +	if (tsk->syscall_intercept)
> >> +		set_tsk_thread_flag(tsk, TIF_SYSCALL_INTERCEPT);
> >> +}
> >
> > Did the above want to be:
> >
> > 	unsigned int old = tsk->syscall_intercept;
> > 	tsk->syscall_intercept |= type;
> > 	if (!old)
> > 		set_tsk_thread_flag(tsk, TIF_SYSCALL_INTERCEPT)
> >
> 
> Hi Peter,
> 
> Thanks for the review!
> 
> I'm not sure this change gains us anything.  For now,
> __set_tsk_syscall_intercept cannot be called with !type, so both
> versions behave the same, but my version is safe with that scenario.
> This won't be called frequent enough for the extra calls to
> set_tsk_thread_flag matter.  Am I missing something?

Your version will do set_tsk_thread_flag() for every invocation
(assuming non-zero type). That's sub-optimal.
```