Re: hrtimer: one more expiry time overflow check in hrtimer_interrupt

[Prarit Bhargava]

On 06/11/2013 03:41 AM, Shinya Kuribayashi wrote:
> When executing a date command to set the system date and time to a few
> seconds before the 2038 problem expiration time, we got a WARN_ON_ONCE()
> like this:
> 
>   root@renesas:~# date -s "2038-1-19 3:14:00"
>   Tue Jan 19 03:14:00 GMT 2038
>   (then wait for 7-8 seconds)
>   root@renesas:~# [   27.662658] ------------[ cut here ]------------
>   [   27.667297] WARNING: at kernel/time/clockevents.c:209 clockevents_program_event+0x3c/0x138()
>   [   27.675720] Modules linked in:
>   [   27.678802] [<c00130ec>] (unwind_backtrace+0x0/0xe0) from [<c001f4d8>] (warn_slowpath_common+0x4c/0x64)
>   [   27.688201] [<c001f4d8>] (warn_slowpath_common+0x4c/0x64) from [<c001f508>] (warn_slowpath_null+0x18/0x1c)
>   [   27.697845] [<c001f508>] (warn_slowpath_null+0x18/0x1c) from [<c00549bc>] (clockevents_program_event+0x3c/0x138)
>   [   27.708007] [<c00549bc>] (clockevents_program_event+0x3c/0x138) from [<c005510c>] (tick_program_event+0x2c/0x34)
>   [   27.718170] [<c005510c>] (tick_program_event+0x2c/0x34) from [<c003fa98>] (hrtimer_interrupt+0x268/0x2a8)
>   [   27.727752] [<c003fa98>] (hrtimer_interrupt+0x268/0x2a8) from [<c00180c8>] (cmt_timer_interrupt+0x2c/0x34)
>   [   27.737396] [<c00180c8>] (cmt_timer_interrupt+0x2c/0x34) from [<c0066748>] (handle_irq_event_percpu+0xb0/0x2a8)
>   [   27.747467] [<c0066748>] (handle_irq_event_percpu+0xb0/0x2a8) from [<c0066998>] (handle_irq_event+0x58/0x74)
>   [   27.757293] [<c0066998>] (handle_irq_event+0x58/0x74) from [<c0068f24>] (handle_fasteoi_irq+0xc0/0x148)
>   [   27.766662] [<c0068f24>] (handle_fasteoi_irq+0xc0/0x148) from [<c0066014>] (generic_handle_irq+0x20/0x30)
>   [   27.776245] [<c0066014>] (generic_handle_irq+0x20/0x30) from [<c000ef54>] (handle_IRQ+0x60/0x84)
>   [   27.785003] [<c000ef54>] (handle_IRQ+0x60/0x84) from [<c0009334>] (gic_handle_irq+0x34/0x4c)
>   [   27.793426] [<c0009334>] (gic_handle_irq+0x34/0x4c) from [<c000e2c0>] (__irq_svc+0x40/0x70)
>   [   27.801788] Exception stack(0xc04aff68 to 0xc04affb0)
>   [   27.806823] ff60:                   00000000 f0100000 00000001 00000000 c04ae000 c04ec388
>   [   27.815002] ff80: c04b604c c0840d80 40004059 412fc093 00000000 00000000 c04ce140 c04affb0
>   [   27.823150] ffa0: c000f064 c000f068 60000013 ffffffff
>   [   27.828216] [<c000e2c0>] (__irq_svc+0x40/0x70) from [<c000f068>] (default_idle+0x24/0x2c)
>   [   27.836395] [<c000f068>] (default_idle+0x24/0x2c) from [<c000f338>] (cpu_idle+0x74/0xc8)
>   [   27.844451] [<c000f338>] (cpu_idle+0x74/0xc8) from [<c048c6d4>] (start_kernel+0x248/0x288)
>   [   27.852722] ---[ end trace 9d8ad385bde80fd3 ]---


>   [   27.857330] hrtimer: interrupt took 0 ns

^^^ see below ...

> 
> This is triggered with our v3.4-based custom ARM kernel, but we
> confirmed that v3.10-rc can still have the same problem.
> 
> I found a similar issue fixed in v3.9 by Prarit Bhargava in commit
> 8f294b5a13 (hrtimer: Add expiry time overflow check in hrtimer_interrupt,
> 2013-04-08).  It tried to resolve a overflow issue detected around 1970
> + 100 seconds.
> 
> On the other hand, we have another call site of tick_program_event() at
> the bottom of hrtimer_interrupt().  The warning this time is triggered
> there, so we need to apply the same fix to it.
> 
> Reported-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@xxxxxxxxxxx>
> Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi.px@xxxxxxxxxxx>
> ---
> 
> Hi Prarit-san and John-san,
> 
> http://git.kernel.org/linus/8f294b5a139ee4b75e890ad5b443c93d1e558a8b
> hrtimer: Add expiry time overflow check in hrtimer_interrupt
> 
> I tried to fix the other case of overflow issues in hrtimer_interrupt(),
> but not sure it should be worked around like this in the first place.
> 
> Any comments are appreciated, thanks in advance.
> 
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index cdd5607..a42d712 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -1368,6 +1370,8 @@ retry:
>  		expires_next = ktime_add_ns(now, 100 * NSEC_PER_MSEC);
>  	else
>  		expires_next = ktime_add(now, delta);
> +	if (expires_next.tv64 < 0)
> +		expires_next.tv64 = KTIME_MAX;

Even with this change you will still see the warning below if delta = 0.

>  	tick_program_event(expires_next, 1);
>  	printk_once(KERN_WARNING "hrtimer: interrupt took %llu ns\n",
>  		    ktime_to_ns(delta));

So I'm not sure that this is the correct thing to do.

Is this reproducible on any ARM system?  I'll grab an x86_64 box and give it a
shot there too.  Can you dump the values of now, delta, and expires_next when
the printk_once triggers?

P.
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