Thread: [uml-devel] UML regression with latest RC 4.11-rc2

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Hi list, hi Richard

There is an extra check in mm/mmap.c which now throws a WARN on every 
page in making UML unusable with the latest 4.11-rc2

A.

Anton,

On Fri, Mar 17, 2017 at 8:51 AM, Anton Ivanov
<ant...@ko...> wrote:
> Hi list, hi Richard
>
> There is an extra check in mm/mmap.c which now throws a WARN on every
> page in making UML unusable with the latest 4.11-rc2

Which WARN? Can you find the offending commit?

-- 
Thanks,
//richard

On 17/03/17 16:56, Richard Weinberger wrote:
> Anton,
>
> On Fri, Mar 17, 2017 at 8:51 AM, Anton Ivanov
> <ant...@ko...> wrote:
>> Hi list, hi Richard
>>
>> There is an extra check in mm/mmap.c which now throws a WARN on every
>> page in making UML unusable with the latest 4.11-rc2
> Which WARN? Can you find the offending commit?

mm/mmap.c line 1112

I spent the day polishing the epoll patch so have not had the time to 
look at this.

It works fine with the 3 warns there commented out.

A.

>

Anton,

Am 17.03.2017 um 18:04 schrieb Anton Ivanov:
> On 17/03/17 16:56, Richard Weinberger wrote:
>> Anton,
>>
>> On Fri, Mar 17, 2017 at 8:51 AM, Anton Ivanov
>> <ant...@ko...> wrote:
>>> Hi list, hi Richard
>>>
>>> There is an extra check in mm/mmap.c which now throws a WARN on every
>>> page in making UML unusable with the latest 4.11-rc2
>> Which WARN? Can you find the offending commit?
> 
> mm/mmap.c line 1112
> 
> I spent the day polishing the epoll patch so have not had the time to look at this.
> 
> It works fine with the 3 warns there commented out.

Hm, it does not trigger here. Can you share your .config?

Thanks,
//richard

On 17/03/17 17:04, Anton Ivanov wrote:
> On 17/03/17 16:56, Richard Weinberger wrote:
>> Anton,
>>
>> On Fri, Mar 17, 2017 at 8:51 AM, Anton Ivanov
>> <ant...@ko...> wrote:
>>> Hi list, hi Richard
>>>
>>> There is an extra check in mm/mmap.c which now throws a WARN on every
>>> page in making UML unusable with the latest 4.11-rc2
>> Which WARN? Can you find the offending commit?
> mm/mmap.c line 1112
>
> I spent the day polishing the epoll patch so have not had the time to
> look at this.
>
> It works fine with the 3 warns there commented out.

It looks like the culprit is an SMP mmap race fix 
e86f15ee64d8ee46255d964d55f74f5ba9af8c36

A.

>
> A.
>
>
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Am 17.03.2017 um 18:04 schrieb Anton Ivanov:
> On 17/03/17 16:56, Richard Weinberger wrote:
>> Anton,
>>
>> On Fri, Mar 17, 2017 at 8:51 AM, Anton Ivanov
>> <ant...@ko...> wrote:
>>> Hi list, hi Richard
>>>
>>> There is an extra check in mm/mmap.c which now throws a WARN on every
>>> page in making UML unusable with the latest 4.11-rc2
>> Which WARN? Can you find the offending commit?
> 
> mm/mmap.c line 1112

Okay, this triggers since:

commit e86f15ee64d8ee46255d964d55f74f5ba9af8c36
Author: Andrea Arcangeli <aar...@re...>
Date:   Fri Oct 7 17:01:28 2016 -0700

    mm: vma_merge: fix vm_page_prot SMP race condition against rmap_walk

But you have to enable VM debugging to see it.

Thanks,
//richard

On 17/03/17 17:33, Richard Weinberger wrote:
> Am 17.03.2017 um 18:04 schrieb Anton Ivanov:
>> On 17/03/17 16:56, Richard Weinberger wrote:
>>> Anton,
>>>
>>> On Fri, Mar 17, 2017 at 8:51 AM, Anton Ivanov
>>> <ant...@ko...> wrote:
>>>> Hi list, hi Richard
>>>>
>>>> There is an extra check in mm/mmap.c which now throws a WARN on every
>>>> page in making UML unusable with the latest 4.11-rc2
>>> Which WARN? Can you find the offending commit?
>> mm/mmap.c line 1112
> Okay, this triggers since:
>
> commit e86f15ee64d8ee46255d964d55f74f5ba9af8c36
> Author: Andrea Arcangeli <aar...@re...>
> Date:   Fri Oct 7 17:01:28 2016 -0700
>
>     mm: vma_merge: fix vm_page_prot SMP race condition against rmap_walk
>
> But you have to enable VM debugging to see it.

I have most debugging enabled to make sure I do not introduce any
re-entrancy in the IRQ handlers and/or have any allocations of the wrong
type where they do not belong.

We should probably submit a short patch #ifdef to turn this WARN() off
for UML

Brgds,

A.

>
> Thanks,
> //richard
>

Anton,

Am 17.03.2017 um 18:44 schrieb Anton Ivanov:
>> But you have to enable VM debugging to see it.
> 
> I have most debugging enabled to make sure I do not introduce any
> re-entrancy in the IRQ handlers and/or have any allocations of the wrong
> type where they do not belong.
> 
> We should probably submit a short patch #ifdef to turn this WARN() off
> for UML

Not before we understand the root cause. :)

Thanks,
//richard