linux-kernel - Re: [PATCH v4] ipc: Update semtimedop() to use hrtimer

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Date:   Thu, 5 May 2022 06:30:54 +0200
From:   Manfred Spraul <manfred@...orfullife.com>
To:     Prakash Sangappa <prakash.sangappa@...cle.com>,
        linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, akpm@...ux-foundation.org,
        peterz@...radead.org, dave@...olabs.net
Subject: Re: [PATCH v4] ipc: Update semtimedop() to use hrtimer

On 4/29/22 01:18, 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@...cle.com>
> Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
> Reviewed-by: Davidlohr Bueso <dave@...olabs.net>
> ---
> v1->v2:
>    - Use timespec64_valid() to validate timeout
>       and other changes as suggested by Thomas Gleixner
> v2->v3: Added Reviewed by tag (Thomas)
> v3->v4: Added Reviewed by (Davidlohr)
>
>   ipc/sem.c | 23 +++++++++++------------
>   1 file changed, 11 insertions(+), 12 deletions(-)
Reviewed-by: Manfred Spraul <manfred@...orfullife.com>
> diff --git a/ipc/sem.c b/ipc/sem.c
> index 0dbdb98..44b65b6 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -1995,7 +1995,9 @@ long __do_semtimedop(int semid, struct sembuf *sops,
>   	int max, locknum;
>   	bool undos = false, alter = false, dupsop = false;
>   	struct sem_queue queue;
> -	unsigned long dup = 0, jiffies_left = 0;
> +	unsigned long dup = 0;
> +	ktime_t expires, *exp = NULL;
> +	bool timed_out = false;
>   
>   	if (nsops < 1 || semid < 0)
>   		return -EINVAL;
> @@ -2003,12 +2005,11 @@ long __do_semtimedop(int semid, struct sembuf *sops,
>   		return -E2BIG;
>   
>   	if (timeout) {
> -		if (timeout->tv_sec < 0 || timeout->tv_nsec < 0 ||
> -			timeout->tv_nsec >= 1000000000L) {
> -			error = -EINVAL;
> -			goto out;
> -		}
> -		jiffies_left = timespec64_to_jiffies(timeout);
> +		if (!timespec64_valid(timeout))
> +			return -EINVAL;
> +		expires = ktime_add_safe(ktime_get(),
> +				timespec64_to_ktime(*timeout));
> +		exp = &expires;
>   	}
>   
>   
> @@ -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);
>   
>   		/*
>   		 * fastpath: the semop has completed, either successfully or
> @@ -2210,7 +2209,7 @@ long __do_semtimedop(int semid, struct sembuf *sops,
>   		/*
>   		 * If an interrupt occurred we have to clean up the queue.
>   		 */
> -		if (timeout && jiffies_left == 0)
> +		if (timed_out)
>   			error = -EAGAIN;
>   	} while (error == -EINTR && !signal_pending(current)); /* spurious */
>