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

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Message-Id: <20220425135053.a74082b68d26f4f3f0344500@linux-foundation.org>
Date:   Mon, 25 Apr 2022 13:50:53 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Prakash Sangappa <prakash.sangappa@...cle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Manfred Spraul <manfred@...orfullife.com>
Subject: Re: [PATCH] ipc: Update semtimedop() to use hrtimer

On Mon, 25 Apr 2022 19:38:44 +0000 Prakash Sangappa <prakash.sangappa@...cle.com> wrote:

> 
> 
> > On Apr 18, 2022, at 6:51 PM, Prakash Sangappa <prakash.sangappa@...cle.com> 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>
> 
> Can I get a review of this patch?

That would be nice.

I looked at it, seemed OK.  Perhaps the usual IPC developers (Davidlohr
and Manfred) can comment?

> Note this patch has been added to Andrew's mm tree.
> 
> 
> > ---
> > ipc/sem.c | 15 +++++++++++----
> > 1 file changed, 11 insertions(+), 4 deletions(-)
> > 
> > diff --git a/ipc/sem.c b/ipc/sem.c
> > index 0dbdb98..6cd1a1b8 100644
> > --- a/ipc/sem.c
> > +++ b/ipc/sem.c
> > @@ -1995,7 +1995,10 @@ 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;
> > +	int timed_out = 0;
> > +	struct timespec64 end_time;
> > 
> > 	if (nsops < 1 || semid < 0)
> > 		return -EINVAL;
> > @@ -2008,7 +2011,9 @@ long __do_semtimedop(int semid, struct sembuf *sops,
> > 			error = -EINVAL;
> > 			goto out;
> > 		}
> > -		jiffies_left = timespec64_to_jiffies(timeout);
> > +		ktime_get_ts64(&end_time);
> > +		end_time = timespec64_add_safe(end_time, *timeout);
> > +		expires = timespec64_to_ktime(end_time);
> > 	}
> > 
> > 
> > @@ -2167,7 +2172,9 @@ long __do_semtimedop(int semid, struct sembuf *sops,
> > 		rcu_read_unlock();
> > 
> > 		if (timeout)
> > -			jiffies_left = schedule_timeout(jiffies_left);
> > +			timed_out = !schedule_hrtimeout_range(&expires,
> > +						current->timer_slack_ns,
> > +						HRTIMER_MODE_ABS);
> > 		else
> > 			schedule();
> > 
> > @@ -2210,7 +2217,7 @@ 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 (timeout && timed_out)
> > 			error = -EAGAIN;
> > 	} while (error == -EINTR && !signal_pending(current)); /* spurious */
> > 
> > -- 
> > 2.7.4
> > 
>