Hotplug crash fix

Hotplug crash fix

[Mason]

Hello Thomas,

Link to the original report:
https://marc.info/?l=linux-arm-kernel&m=148173152524746&w=2

I do see the two patches in linux-next:

9bf11ecce5a2
c1a9eeb938b5

Shouldn't one or the other (perhaps both?) be back-ported to 4.8
and 4.9?

Regards.

Re: Hotplug crash fix

[Greg Kroah-Hartman]

On Mon, Jan 09, 2017 at 04:53:51PM +0100, Mason wrote:
> Hello Thomas,
> 
> Link to the original report:
> https://marc.info/?l=linux-arm-kernel&m=148173152524746&w=2
> 
> I do see the two patches in linux-next:
> 
> 9bf11ecce5a2
> c1a9eeb938b5

These are both in 4.10-rc1, and I see no reason why I couldn't take them
in stable right now, but I'll wait for Thomas's ack.

thanks,

greg k-h

Re: Hotplug crash fix

[Greg Kroah-Hartman]

On Mon, Jan 09, 2017 at 05:07:06PM +0100, Greg Kroah-Hartman wrote:
> On Mon, Jan 09, 2017 at 04:53:51PM +0100, Mason wrote:
> > Hello Thomas,
> > 
> > Link to the original report:
> > https://marc.info/?l=linux-arm-kernel&m=148173152524746&w=2
> > 
> > I do see the two patches in linux-next:
> > 
> > 9bf11ecce5a2
> > c1a9eeb938b5
> 
> These are both in 4.10-rc1, and I see no reason why I couldn't take them
> in stable right now, but I'll wait for Thomas's ack.

The first one was already in my list to include, the second one is
dirt-simple, so I'll queue it up now as well.

thanks,

greg k-h

Re: Hotplug crash fix

[Mason]

On 10/01/2017 14:13, Greg Kroah-Hartman wrote:
> On Mon, Jan 09, 2017 at 05:07:06PM +0100, Greg Kroah-Hartman wrote:
>> On Mon, Jan 09, 2017 at 04:53:51PM +0100, Mason wrote:
>>> Hello Thomas,
>>>
>>> Link to the original report:
>>> https://marc.info/?l=linux-arm-kernel&m=148173152524746&w=2
>>>
>>> I do see the two patches in linux-next:
>>>
>>> 9bf11ecce5a2
>>> c1a9eeb938b5
>>
>> These are both in 4.10-rc1, and I see no reason why I couldn't take them
>> in stable right now, but I'll wait for Thomas's ack.
> 
> The first one was already in my list to include, the second one is
> dirt-simple, so I'll queue it up now as well.

Thomas,

If the kernel hadn't crashed in tick_broadcast_setup_oneshot()
then the issue of the dummy timer being too early in the list
wouldn't have been caught, right?

So I'm wondering if it didn't make sense to WARN when bc is NULL
in tick_broadcast_setup_oneshot? (Instead of silently bailing out.)

Regards.

Re: Hotplug crash fix

[Thomas Gleixner]

On Tue, 10 Jan 2017, Mason wrote:
> On 10/01/2017 14:13, Greg Kroah-Hartman wrote:
> > On Mon, Jan 09, 2017 at 05:07:06PM +0100, Greg Kroah-Hartman wrote:
> >> On Mon, Jan 09, 2017 at 04:53:51PM +0100, Mason wrote:
> >>> Hello Thomas,
> >>>
> >>> Link to the original report:
> >>> https://marc.info/?l=linux-arm-kernel&m=148173152524746&w=2
> >>>
> >>> I do see the two patches in linux-next:
> >>>
> >>> 9bf11ecce5a2
> >>> c1a9eeb938b5
> >>
> >> These are both in 4.10-rc1, and I see no reason why I couldn't take them
> >> in stable right now, but I'll wait for Thomas's ack.
> > 
> > The first one was already in my list to include, the second one is
> > dirt-simple, so I'll queue it up now as well.
> 
> If the kernel hadn't crashed in tick_broadcast_setup_oneshot()
> then the issue of the dummy timer being too early in the list
> wouldn't have been caught, right?

It's the other way round. If we would have kept that timer late in the list
then we wouldn't have seen the issue that tick_broadcast_setup_oneshot()
missed the NULL pointer check.

The first patch which moves it late was just to restore the state before
the hotplug changes. But that's not a fix at all. The real one is the NULL
pointer check.

I kept that patch because it does not make any sense to install that dummy
timer _before_ all other options are exhausted.

> So I'm wondering if it didn't make sense to WARN when bc is NULL
> in tick_broadcast_setup_oneshot? (Instead of silently bailing out.)

No. If the broadcast device is installed late everything will still work,
while dereferencing a NULL pointer doesn't work at all.

Thanks,

	tglx