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

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Message-ID: <20170725180148.GA24730@kroah.com>
Date:   Tue, 25 Jul 2017 11:01:48 -0700
From:   Greg KH <greg@...ah.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Greg Hackmann <ghackmann@...gle.com>,
        John Stultz <john.stultz@...aro.org>,
        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 Tue, Jul 25, 2017 at 09:00:42AM +0200, Thomas Gleixner wrote:
> On Mon, 24 Jul 2017, Greg KH wrote:
> 
> > 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?
> 
> No. I borked that when I was 'fixing' that DoS issue :(
> 
> Reviewed-by: Thomas Gleixner <tglx@...utronix.de>

Thanks for the review.

Greg, can you provide a version of this for 4.12-stable?  It doesn't
apply there as-is.

thanks,

greg k-h