Re: next-20250825: arc: seqlock.h:876:2: error: implicit declaration of function 'spin_lock' [-Werror=implicit-function-declaration]

[Waiman Long <llong@redhat.com>]

On 8/26/25 8:42 AM, Naresh Kamboju wrote:
> On Tue, 26 Aug 2025 at 12:05, Naresh Kamboju <naresh.kamboju@linaro.org> wrote:
>> The following build warnings / errors noticed with arc defconfig with
>> gcc-9 toolchain.
>>
>> Regression Analysis:
>> - New regression? yes
>> - Reproducibility? yes
>>
>> Build regression: next-20250825 arc seqlock.h:876:2: error: implicit
>> declaration of function 'spin_lock'
>> [-Werror=implicit-function-declaration]
>>
>> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
>>
>> arc:
>>    build:
>>      * gcc-9-allnoconfig
>>      * gcc-9-tinyconfig
>>      * gcc-9-vdk_hs38_smp_defconfig
>>      * gcc-9-defconfig
>>      * gcc-9-axs103_defconfig
>>
>> ## Build log
>> In file included from include/linux/mmzone.h:17,
>>                   from include/linux/gfp.h:7,
>>                   from include/linux/mm.h:7,
>>                   from arch/arc/include/asm/arcregs.h:149,
>>                   from arch/arc/include/asm/irqflags-arcv2.h:9,
>>                   from arch/arc/include/asm/irqflags.h:13,
>>                   from include/linux/irqflags.h:18,
>>                   from include/linux/spinlock.h:59,
>>                   from include/linux/sched.h:37,
>>                   from arch/arc/kernel/asm-offsets.c:6:
>> include/linux/seqlock.h: In function 'write_seqlock':
>> include/linux/seqlock.h:876:2: error: implicit declaration of function
>> 'spin_lock' [-Werror=implicit-function-declaration]
>>    876 |  spin_lock(&sl->lock);
>>        |  ^~~~~~~~~
>> include/linux/seqlock.h: In function 'write_sequnlock':
>> include/linux/seqlock.h:890:2: error: implicit declaration of function
>> 'spin_unlock' [-Werror=implicit-function-declaration]
>>    890 |  spin_unlock(&sl->lock);
>>        |  ^~~~~~~~~~~
>> include/linux/seqlock.h: In function 'write_seqlock_bh':
>> include/linux/seqlock.h:902:2: error: implicit declaration of function
>> 'spin_lock_bh' [-Werror=implicit-function-declaration]
>>    902 |  spin_lock_bh(&sl->lock);
>>        |  ^~~~~~~~~~~~
>> include/linux/seqlock.h: In function 'write_sequnlock_bh':
>> include/linux/seqlock.h:917:2: error: implicit declaration of function
>> 'spin_unlock_bh' [-Werror=implicit-function-declaration]
>>    917 |  spin_unlock_bh(&sl->lock);
>>        |  ^~~~~~~~~~~~~~
>> include/linux/seqlock.h: In function 'write_seqlock_irq':
>> include/linux/seqlock.h:929:2: error: implicit declaration of function
>> 'spin_lock_irq' [-Werror=implicit-function-declaration]
>>    929 |  spin_lock_irq(&sl->lock);
>>        |  ^~~~~~~~~~~~~
>> include/linux/seqlock.h: In function 'write_sequnlock_irq':
>> include/linux/seqlock.h:943:2: error: implicit declaration of function
>> 'spin_unlock_irq'; did you mean 'write_sequnlock_irq'?
>> [-Werror=implicit-function-declaration]
>>    943 |  spin_unlock_irq(&sl->lock);
>>        |  ^~~~~~~~~~~~~~~
>>        |  write_sequnlock_irq
>> include/linux/seqlock.h: In function '__write_seqlock_irqsave':
>> include/linux/seqlock.h:950:2: error: implicit declaration of function
>> 'spin_lock_irqsave' [-Werror=implicit-function-declaration]
>>    950 |  spin_lock_irqsave(&sl->lock, flags);
>>        |  ^~~~~~~~~~~~~~~~~
>> include/linux/seqlock.h: In function 'write_sequnlock_irqrestore':
>> include/linux/seqlock.h:981:2: error: implicit declaration of function
>> 'spin_unlock_irqrestore'; did you mean 'write_sequnlock_irqrestore'?
>> [-Werror=implicit-function-declaration]
>>    981 |  spin_unlock_irqrestore(&sl->lock, flags);
>>        |  ^~~~~~~~~~~~~~~~~~~~~~
>>        |  write_sequnlock_irqrestore
>> In file included from include/linux/sched.h:15,
>>                   from arch/arc/kernel/asm-offsets.c:6:
>> include/linux/rcupdate.h: In function 'rcu_read_lock_sched_held':
>> include/linux/preempt.h:227:49: error: implicit declaration of
>> function 'irqs_disabled' [-Werror=implicit-function-declaration]
>>    227 | #define preemptible() (preempt_count() == 0 && !irqs_disabled())
>>        |                                                 ^~~~~~~~~~~~~
>>                            ^
>> cc1: some warnings being treated as errors
> Anders bisected this and found,
>   # first bad commit:
>     [7cf258e5720ffdd5505faa04ab5afa9732ef0f6e]
>     mm-replace-20-page_shift-with-common-macros-for-pages-mb-conversion-fix

The compilation problem is a result of bad include file ordering. Since 
the only users of PAGES_TO_MB() macro are kernel/rcu/rcuscale.c and 
mm/swap.c and they both include <linux/mm.h>. So this can be fixed by 
just removing the <linux/mm.h> include from arcregs.h.

Cheers,
Longman


>> ## Source
>> * Kernel version: 6.17.0-rc3-next-20250825
>> * Git tree: https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next.git
>> * Git describe: next-20250825
>> * Git commit: 6c68f4c0a147c025ae0b25fab688c7c47964a02f
>> * Architectures: arc
>> * Toolchains: gcc-9
>> * Kconfigs: defconfig
>>
>> ## Build
>> * Build log: https://qa-reports.linaro.org/api/testruns/29652436/log_file/
>> * Build details:
>> https://regressions.linaro.org/lkft/linux-next-master/next-20250825/build/gcc-9-defconfig/
>> * Build error details:
>> https://regressions.linaro.org/lkft/linux-next-master/next-20250825/log-parser-build-gcc/gcc-compiler-include_asm-generic_getorder_h-error-implicit-declaration-of-function-ilog/
>> * Build plan: https://tuxapi.tuxsuite.com/v1/groups/linaro/projects/lkft/builds/31lrYki7MzYyqtJKnutAe2oawoq
>> * Build link: https://storage.tuxsuite.com/public/linaro/lkft/builds/31lrYki7MzYyqtJKnutAe2oawoq/
>> * Kernel config:
>> https://storage.tuxsuite.com/public/linaro/lkft/builds/31lrYki7MzYyqtJKnutAe2oawoq/config
>>
>> --
>> Linaro LKFT
>> https://lkft.linaro.org