linux-kernel - Re: [PATCH] timers: Fix usleep_range() in the context of wake_up

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Date:   Mon, 10 Oct 2016 13:12:39 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        Tao Huang <huangtao@...k-chips.com>,
        Tony Xie <tony.xie@...k-chips.com>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andreas Mohr <andi@...as.de>
Subject: Re: [PATCH] timers: Fix usleep_range() in the context of wake_up_process()

Hi,

On Mon, Oct 10, 2016 at 1:04 PM, Brian Norris <briannorris@...omium.org> wrote:
> Hi Doug,
>
> On Mon, Oct 10, 2016 at 11:47:57AM -0700, Doug Anderson wrote:
>> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
>> index 32bf6f75a8fe..ab03c7e403a4 100644
>> --- a/kernel/time/timer.c
>> +++ b/kernel/time/timer.c
>> @@ -1898,12 +1898,29 @@ EXPORT_SYMBOL(msleep_interruptible);
>>
>>  static void __sched do_usleep_range(unsigned long min, unsigned long max)
>>  {
>> +     ktime_t start, end;
>>       ktime_t kmin;
>>       u64 delta;
>> +     unsigned long elapsed = 0;
>> +     int ret;
>> +
>> +     start = ktime_get();
>> +     do {
>> +             kmin = ktime_set(0, min * NSEC_PER_USEC);
>
> I believe 'min' is unmodified throughout, and therefore 'kmin' is
> computed to be the same minimum timeout in each loop. Shouldn't this be
> decreasing on each iteration of the loop? (i.e., either your compute
> 'kmin' differently here, or you recompute 'min' based on the elapsed
> time?)

Yes, I stupidly changed something at the last second and then didn't
test again after my stupid change.  Fix coming soon with all comments
addressed.  Sorry for posting broken code.  :( :( :(

-Doug