Re: linux-next: Tree for Sep 16 (kernel/sched/core.c)

[Randy Dunlap]

On 9/18/19 3:03 AM, Patrick Bellasi wrote:
> 
> On Wed, Sep 18, 2019 at 07:05:53 +0100, Ingo Molnar wrote...
> 
>> * Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
>>
>>> On 9/17/19 6:38 AM, Patrick Bellasi wrote:
>>>>
>>>> On Tue, Sep 17, 2019 at 08:52:42 +0100, Ingo Molnar wrote...
>>>>
>>>>> * Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
>>>>>
>>>>>> On 9/16/19 3:38 PM, Mark Brown wrote:
>>>>>>> Hi all,
>>>>>>>
>>>>>>> Changes since 20190915:
>>>>>>>
>>>>>>
>>>>>> on x86_64:
>>>>>>
>>>>>> when CONFIG_CGROUPS is not set:
>>>>
>>>> Hi Randy,
>>>> thanks for the report.
>>>>
>>>>>>   CC      kernel/sched/core.o
>>>>>> ../kernel/sched/core.c: In function âuclamp_update_active_tasksâ:
>>>>>> ../kernel/sched/core.c:1081:23: error: storage size of âitâ isnât known
>>>>>>   struct css_task_iter it;
>>>>>>                        ^~
>>>>>>   CC      kernel/printk/printk_safe.o
>>>>>> ../kernel/sched/core.c:1084:2: error: implicit declaration of function âcss_task_iter_startâ; did you mean â__sg_page_iter_startâ? [-Werror=implicit-function-declaration]
>>>>>>   css_task_iter_start(css, 0, &it);
>>>>>>   ^~~~~~~~~~~~~~~~~~~
>>>>>>   __sg_page_iter_start
>>>>>> ../kernel/sched/core.c:1085:14: error: implicit declaration of function âcss_task_iter_nextâ; did you mean â__sg_page_iter_nextâ? [-Werror=implicit-function-declaration]
>>>>>>   while ((p = css_task_iter_next(&it))) {
>>>>>>               ^~~~~~~~~~~~~~~~~~
>>>>>>               __sg_page_iter_next
>>>>>> ../kernel/sched/core.c:1091:2: error: implicit declaration of function âcss_task_iter_endâ; did you mean âget_task_credâ? [-Werror=implicit-function-declaration]
>>>>>>   css_task_iter_end(&it);
>>>>>>   ^~~~~~~~~~~~~~~~~
>>>>>>   get_task_cred
>>>>>> ../kernel/sched/core.c:1081:23: warning: unused variable âitâ [-Wunused-variable]
>>>>>>   struct css_task_iter it;
>>>>>>                        ^~
>>>>>>
>>>>>
>>>>> I cannot reproduce this build failue: I took Linus's latest which has all 
>>>>> the -next scheduler commits included (ad062195731b), and an x86-64 "make 
>>>>> defconfig" and a disabling of CONFIG_CGROUPS still resuls in a kernel 
>>>>> that builds fine.
>>>>
>>>> Same here Ingo, I cannot reproduce on arm64 and !CONFIG_CGROUPS and
>>>> testing on tip/sched/core.
>>>>
>>>> However, if you like, the following patch can make that code a
>>>> bit more "robust".
>>>>
>>>> Best,
>>>> Patrick
>>>>
>>>> ---8<---
>>>> From 7e17b7bb08dd8dfc57e01c2a7b6875439eb47cbe Mon Sep 17 00:00:00 2001
>>>> From: Patrick Bellasi <patrick.bellasi@xxxxxxx>
>>>> Date: Tue, 17 Sep 2019 14:12:10 +0100
>>>> Subject: [PATCH 1/1] sched/core: uclamp: Fix compile error on !CONFIG_CGROUPS
>>>>
>>>> Randy reported a compiler error on x86_64 and !CONFIG_CGROUPS which is due
>>>> to uclamp_update_active_tasks() using the undefined css_task_iter().
>>>>
>>>> Since uclamp_update_active_tasks() is used only when cgroup support is
>>>> enabled, fix that by properly guarding that function at compile time.
>>>>
>>>> Signed-off-by: Patrick Bellasi <patrick.bellasi@xxxxxxx>
>>>> Link: https://lore.kernel.org/lkml/1898d3c9-1997-17ce-a022-a5e28c8dc115@xxxxxxxxxxxxx/
>>>> Fixes: commit babbe170e05 ("sched/uclamp: Update CPU's refcount on TG's clamp changes")
>>>
>>> Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> # build-tested
>>>
>>> Thanks.
>>
>> Build failures like this one shouldn't depend on the compiler version - 
>> and it's still a mystery how and why this build bug triggered - we cannot 
>> apply the fix without knowing the answer to those questions.
> 
> Right, but it's also quite strange it's not triggering without the
> guarding above. The only definition of struct css_task_iter I can see is
> the one
> provided in:
> 
>    include/linux/cgroup.h:50
>    https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/cgroup.h?h=35f7a95266153b1cf0caca3aa9661cb721864527#n50
> 
> which is CONFIG_CGROUPS guarded.
> 
>> Can you reproduce the build bug with Linus's latest tree? If not, which 
>> part of -next triggers the build failure?
> 
> I tried again using this morning's Linus tree headed at:
> 
>   commit 35f7a9526615 ("Merge tag 'devprop-5.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm")
> 
> and compilation actually fails for me too.

and linux-next of 20190924 still fails also...


> Everything is fine in v5.3 with !CONFIG_CGROUPS and a git bisect
> between v5.3 and Linus master points to:
> 
>   commit babbe170e053c ("sched/uclamp: Update CPU's refcount on TG's clamp changes")
> 
> So, I think it's really my fault not properly testing !CONFIG_CGROUP,
> which is enforced by default from CONFIG_SCHED_AUTOGROUP.
> 
> The patch above fixes the compilation error, hope this helps.
> 
> Cheers,
> Patrick


-- 
~Randy