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

From: Greg Hackmann
Date: Mon Jul 24 2017 - 17:41:32 EST


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")

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.)