linux-kernel - Re: [PATCH] alarmtimer: don't rate limit one-shot timers

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Message-ID: <20170724215544.GA20404@kroah.com>
Date:   Mon, 24 Jul 2017 14:55:44 -0700
From:   Greg KH <greg@...ah.com>
To:     Greg Hackmann <ghackmann@...gle.com>
Cc:     John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ben Fennema <fennema@...gle.com>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] alarmtimer: don't rate limit one-shot timers

On Mon, Jul 24, 2017 at 02:41:10PM -0700, Greg Hackmann wrote:
> On 07/24/2017 11:21 AM, Greg KH wrote:
> > On Mon, Jul 24, 2017 at 10:19:24AM -0700, Greg Hackmann wrote:
> > > Commit ff86bf0c65f1 ("alarmtimer: Rate limit periodic intervals") sets a
> > > minimum bound on the alarm timer interval.  This minimum bound shouldn't
> > > be applied if the interval is 0.  Otherwise, one-shot timers will be
> > > converted into periodic ones.
> > > 
> > > This patch is against 4.9.39, and is only needed in -stable trees.
> > > 4.13-rc2 isn't impacted due to a later refactoring.
> > 
> > What refactoring patch fixed this up?
> 
> f2c45807d399 ("alarmtimer: Switch over to generic set/get/rearm routine")

Ick, yeah, that's not a stable patch :)

> > As this was a 4.12 patch, 4.12-stable needs this fix as well, right?
> 
> Looks like it, but I haven't actually tried 4.12 yet to confirm.
> 
> > Also, was there some test-case that you caught this with that perhaps
> > could be added to LTP or kselftests?
> 
> Unfortunately not a direct testcase.  This first showed up as a regression
> in AOSP's userspace Bluetooth stack, which uses CLOCK_BOOTTIME_ALARM
> internally.
> 
> I'm working on a patch to add one-shot timer testcases to set-timer-lat.c,
> which would have caught this.  (I wrote a very rough test program to make
> sure this patch fixes the regression, but set-timer-lat.c already exists and
> is more comprehensive.)

Ok, thanks for the information.

John and Thomas, any objection for me to take the original patch here in
the stable trees to fix this issue?

thanks,

greg k-h