linux-kernel - Re: restart_syscall: use freezable blocking call

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Message-ID: <20150331150730.GJ23123@twins.programming.kicks-ass.net>
Date:	Tue, 31 Mar 2015 17:07:30 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	maninder1.s@...sung.com, tglx@...utronix.de,
	Yogesh Narayan Gaur <yn.gaur@...sung.com>,
	AJEET YADAV <ajeet.y@...sung.com>, Tejun Heo <tj@...nel.org>
Subject: Re: restart_syscall: use freezable blocking call

On Tue, Mar 31, 2015 at 01:39:07AM +0200, Rafael J. Wysocki wrote:
> > From: Maninder Singh <maninder1.s@...sung.com>
> > Subject: kernel/time/hrtimer.c: restart_syscall: use freezable blocking call
> > 
> > Avoid waking up every thread sleeping in a restart_syscall call during
> > suspend and resume by calling a freezable blocking call.  Previous patches
> > modified the freezer to avoid sending wakeups to threads that are blocked
> > in freezable blocking calls.

This is what, no why mentioned.

> > 
> > Signed-off-by: Yogesh Gaur <yn.gaur <at> samsung.com>
> > Signed-off-by: Amit Arora <amit.arora <at> samsung.com>

This SoB chain is garbage. Most important, note that the author (From by
lack of Author) didn't actually sign off on it.

> > Reviewed-by : Ajeet Yadav <ajeet.y <at> samsung.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> > ---
> > 
> >  kernel/time/hrtimer.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff -puN kernel/time/hrtimer.c~restart_syscall-use-freezable-blocking-call kernel/time/hrtimer.c
> > --- a/kernel/time/hrtimer.c~restart_syscall-use-freezable-blocking-call
> > +++ a/kernel/time/hrtimer.c
> > @@ -1767,7 +1767,7 @@ schedule_hrtimeout_range_clock(ktime_t *
> >  	 * A NULL parameter means "infinite"
> >  	 */
> >  	if (!expires) {
> > -		schedule();
> > +		freezable_schedule();
> >  		return -EINTR;
> >  	}
> >  
> > @@ -1781,7 +1781,7 @@ schedule_hrtimeout_range_clock(ktime_t *
> >  		t.task = NULL;
> >  
> >  	if (likely(t.task))
> > -		schedule();
> > +		freezable_schedule();
> >  
> >  	hrtimer_cancel(&t.timer);
> >  	destroy_hrtimer_on_stack(&t.timer);

Not a single word on why this would be correct. At the very least show
us you've thought about it.
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