Re: [PATCH v3] ipc: Update semtimedop() to use hrtimer

[Davidlohr Bueso]

On Thu, 28 Apr 2022, Prakash Sangappa wrote:

> semtimedop() should be converted to use hrtimer like it has been done
> for most of the system calls with timeouts. This system call already
> takes a struct timespec as an argument and can therefore provide finer
> granularity timed wait.
>
> Signed-off-by: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx>
> Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
> v1->v2:
>  - Use timespec64_valid() to validate timeout
>     and other changes as suggested by Thomas Gleixner
> v2-v3 Added Reviewed by tag
> ---

The second '---' is not necesary, it's the first one that counts.

> @@ -2166,10 +2167,8 @@ long __do_semtimedop(int semid, struct sembuf *sops,
> 		sem_unlock(sma, locknum);
> 		rcu_read_unlock();
>
> -		if (timeout)
> -			jiffies_left = schedule_timeout(jiffies_left);
> -		else
> -			schedule();
> +		timed_out = !schedule_hrtimeout_range(exp,
> +				current->timer_slack_ns, HRTIMER_MODE_ABS);

I'm wondering if the slack parameter instead of passing the timer_slack_ns
value immediately, we should do a rt_task() check and pass zero if so.
And the opposite for the posix mqueue case: bit a little more lenient when
!rt_task() and pass current->timer_slack_ns instead of zero. Of course mq
is a lot more rt aware than sysv semaphores, but that doesn't mean both forms
of ipc are not seen used with or without RT constraints.

Thanks,
Davidlohr