Re: linux-next: build warning after merge of the net-next tree

[Masahiro Yamada <yamada.masahiro@socionext.com>]

2018-07-20 8:19 GMT+09:00 Masahiro Yamada <yamada.masahiro@socionext.com>:
> 2018-07-20 7:35 GMT+09:00 Guenter Roeck <linux@roeck-us.net>:
>> On Fri, Jul 20, 2018 at 08:09:06AM +1000, Stephen Rothwell wrote:
>>> Hi Guenter,
>>>
>>> On Thu, 19 Jul 2018 06:49:01 -0700 Guenter Roeck <linux@roeck-us.net> wrote:
>>> >
>>> > On 07/18/2018 10:29 PM, Stephen Rothwell wrote:
>>> > >
>>> > > On Wed, 18 Jul 2018 20:52:56 -0700 Guenter Roeck <linux@roeck-us.net> wrote:
>>> > >>
>>> > >> On 07/18/2018 07:04 PM, Stephen Rothwell wrote:
>>> > >>>
>>> > >>> After merging the net-next tree, today's linux-next build (x86_64
>>> > >>> allmodconfig) produced this warning:
>>> > >>>
>>> > >>> *
>>> > >>> * Restart config...
>>> > >>> *
>>> > >>> ....
>>> > >>>
>>> > >>> This is output by my "make allmodconfig" and only started after merging
>>> > >>> the net-next tree today.  It has continued for further merges/builds.
>>> > >>>
>>> > >>> I suspect commit
>>> > >>>
>>> > >>>     1323061a018a ("net: phy: sfp: Add HWMON support for module sensors")
>>> > >>>
>>> > >>> which added an "imply" clause.
>>> > >>>
>>> > >> I thought "imply" was better than "depends on HWMON || HWMON=n", but maybe
>>> > >> not. Is that a caveat when using "imply", and does it mean that "imply"
>>> > >> should better not be used ?
>>> > >
>>> > > I don't know, sorry.  It was just my best guess from what I could see
>>> > > had changed.
>>> > >
>>> > > I wonder if it makes a difference that I am doing my "make
>>> > > allmodconfig" on top of a previous "make allmodconfig" and some symbols
>>> > > are marked as "NEW" (though they are not symbols related to the changes
>>> > > that happened during the net-next tree merge)?
>>> > >
>>> >
>>> > I tried to reproduce the problem, but I don't see the message.
>>> >
>>> > What I do see, though, is that "make allmodconfig" on a clean tree,
>>> > followed by "make menuconfig", results in configuration changes.
>>> > Specifically,
>>> >
>>> >  > CONFIG_ARC_EMAC_CORE=m
>>> >  > CONFIG_ARC_EMAC=m
>>> >  > CONFIG_EMAC_ROCKCHIP=m
>>> >
>>> > is removed by menuconfig, and a large number of "# ... is not set"
>>> > configuration lines are added. Weird and bad, since several of the
>>> > disabled configurations _should_ be enabled by "make allmodconfig",
>>> > and a large number of hwmon drivers are affected. Bisect does point
>>> > to "net: phy: sfp: Add HWMON support for module sensors", meaning
>>> > "imply hwmon" does have severe side effects and can not be used.
>>> >
>>> > I'll try to find a fix.
>>>
>>> OK, my mistake, the "make allmodconfig" works, the following "make"
>>> causes the config restart.  (I am actually doing cross builds and using
>>> an external object directory, in case that matters.)
>>>
>>> I removed the "imply HWMON" line added by the above commit and the
>>> problem went away.  Also, using "depends on HWMON || HWMON=n" instead
>>> of the imply fixes it.
>>
>> Yes, replacing imply with the dependency is what I did in the fixup patch.
>> Sorry, I should have copied you: https://patchwork.kernel.org/patch/10534925/
>>
>> It is a bit different - imply was supposed to enforce HWMON={y,n} if SFP=y,
>> and the depends line enforces SFP={n,m} if HWMON=m. I have no idea why
>> imply doesn't work, but I think I'll stay away from it in the future.
>>
>> Guenter
>
>
> Hmm, this could be a Kconfig bug.
>
> I will take a look.


Today, I took a look at it.

The cause of the problem was the circular dependency.

Somehow, 'imply' is not checked in the circular dependency.

So, I wrote patches to report this.
https://patchwork.kernel.org/patch/10565061/
https://patchwork.kernel.org/patch/10565063/


If you apply those two patches on top of commit
1323061a018a ("net: phy: sfp: Add HWMON support for module sensors")
It is reported in allmodconfig stage, like this:


masahiro@grover:~/ref/linux-next$ make allmodconfig
  HOSTCC  scripts/kconfig/conf.o
  YACC    scripts/kconfig/zconf.tab.c
  HOSTCC  scripts/kconfig/zconf.tab.o
  HOSTLD  scripts/kconfig/conf
scripts/kconfig/conf  --allmodconfig Kconfig
drivers/of/Kconfig:68:error: recursive dependency detected!
drivers/of/Kconfig:68: symbol OF_IRQ depends on IRQ_DOMAIN
kernel/irq/Kconfig:63: symbol IRQ_DOMAIN is selected by REGMAP
drivers/base/regmap/Kconfig:6: symbol REGMAP is selected by SENSORS_ASPEED
drivers/hwmon/Kconfig:352: symbol SENSORS_ASPEED depends on HWMON
drivers/hwmon/Kconfig:5: symbol HWMON is implied by SFP
drivers/net/phy/Kconfig:214: symbol SFP depends on PHYLIB
drivers/net/phy/Kconfig:181: symbol PHYLIB is selected by ARC_EMAC_CORE
drivers/net/ethernet/arc/Kconfig:18: symbol ARC_EMAC_CORE is selected
by ARC_EMAC
drivers/net/ethernet/arc/Kconfig:24: symbol ARC_EMAC depends on OF_IRQ
For a resolution refer to Documentation/kbuild/kconfig-language.txt
subsection "Kconfig recursive dependency limitations"

#
# configuration written to .config
#




>
>
> BTW,
> 'depends on HWMON || HWMON=n' is pointless
> because it is always true.



-- 
Best Regards
Masahiro Yamada