Build failure in nvram.c due to unused nvram_mutex (-Werror) on 7.1.0-rc1 upstream kernel

[vpuliyal]

Description

Kernel build fails while compiling nvram.c due to an unused variable.

Error

nvram.c:56:21: error: 'nvram_mutex' defined but not used [-Werror=unused-variable]

Steps to Reproduce

make -j81 -s

Expected Behavior

Build should complete successfully.

Actual Behavior

Build fails due to -Werror treating warning as error.

[console-expect]#make -j 81 -s && make modules_install && make install
make -j 81 -s && make modules_install && make install
In file included from ^[[01m^[[K./include/linux/seqlock.h:20^[[m^[[K,
                 from ^[[01m^[[K./include/linux/mmzone.h:17^[[m^[[K,
                 from ^[[01m^[[K./include/linux/gfp.h:7^[[m^[[K,
                 from ^[[01m^[[K./include/linux/umh.h:4^[[m^[[K,
                 from ^[[01m^[[K./include/linux/kmod.h:9^[[m^[[K,
                 from ^[[01m^[[K./include/linux/module.h:18^[[m^[[K,
                 from ^[[01m^[[Kdrivers/char/nvram.c:34^[[m^[[K:
^[[01m^[[Kdrivers/char/nvram.c:56:21:^[[m^[[K ^[[01;31m^[[Kerror: ^[[m^[[K'^[[01m^[[Knvram_mutex^[[m^[[K' defined but not used [^[[01;31m^[[K^[]8;;https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wunused-variable^G-Werror=unused-variable^[]8;;^G^[[m^[[K]
   56 | static DEFINE_MUTEX(^[[01;31m^[[Knvram_mutex^[[m^[[K);
      |                     ^[[01;31m^[[K^~~~~~~~~~~^[[m^[[K
^[[01m^[[K./include/linux/mutex.h:87:22:^[[m^[[K ^[[01;36m^[[Knote: ^[[m^[[Kin definition of macro '^[[01m^[[KDEFINE_MUTEX^[[m^[[K'
   87 |         struct mutex ^[[01;36m^[[Kmutexname^[[m^[[K = __MUTEX_INITIALIZER(mutexname)
      |                      ^[[01;36m^[[K^~~~~~~~~^[[m^[[K
cc1: all warnings being treated as errors
make[4]: *** [scripts/Makefile.build:289: drivers/char/nvram.o] Error 1
make[4]: *** Waiting for unfinished jobs....
make[3]: *** [scripts/Makefile.build:548: drivers/char] Error 2
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [scripts/Makefile.build:548: drivers] Error 2
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [/home/linux_src/linux/Makefile:2141: .] Error 2
make: *** [Makefile:248: __sub-make] Error 2
[console-expect]#echo $?
echo $?
2
ERROR

======================================================================
ERROR: runTest (testcases.InstallUpstreamKernel.InstallUpstreamKernel)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/var/lib/jenkins/workspace/LTC/op-test/testcases/InstallUpstreamKernel.py", line 130, in runTest
    con.run_command("make -j %d -s && make modules_install && make install" %
  File "/var/lib/jenkins/workspace/LTC/op-test/common/OpTestSSH.py", line 225, in run_command
    return self.util.run_command(self, command, timeout, retry)
  File "/var/lib/jenkins/workspace/LTC/op-test/common/OpTestUtil.py", line 1820, in run_command
    raise cf
  File "/var/lib/jenkins/workspace/LTC/op-test/common/OpTestUtil.py", line 1815, in run_command
    output = self.try_command(term_obj, command, timeout)
  File "/var/lib/jenkins/workspace/LTC/op-test/common/OpTestUtil.py", line 1890, in try_command
    raise CommandFailed(command, res, echo_rc)
common.Exceptions.CommandFailed: Command 'make -j 81 -s && make modules_install && make install' exited with '2'.
Output
['In file included from \x1b[01m\x1b[K./include/linux/seqlock.h:20\x1b[m\x1b[K,', '                 from \x1b[01m\x1b[K./include/linux/mmzone.h:17\x1b[m\x1b[K,', '                 from \x1b[01m\x1b[K./include/linux/gfp.h:7\x1b[m\x1b[K,', '                 from \x1b[01m\x1b[K./include/linux/umh.h:4\x1b[m\x1b[K,', '                 from \x1b[01m\x1b[K./include/linux/kmod.h:9\x1b[m\x1b[K,', '                 from \x1b[01m\x1b[K./include/linux/module.h:18\x1b[m\x1b[K,', '                 from \x1b[01m\x1b[Kdrivers/char/nvram.c:34\x1b[m\x1b[K:', "\x1b[01m\x1b[Kdrivers/char/nvram.c:56:21:\x1b[m\x1b[K \x1b[01;31m\x1b[Kerror: \x1b[m\x1b[K'\x1b[01m\x1b[Knvram_mutex\x1b[m\x1b[K' defined but not used [\x1b[01;31m\x1b[K\x1b]8;;https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wunused-variable\x07-Werror=unused-variable\x1b]8;;\x07\x1b[m\x1b[K]", '   56 | static DEFINE_MUTEX(\x1b[01;31m\x1b[Knvram_mutex\x1b[m\x1b[K);', '      |                     \x1b[01;31m\x1b[K^~~~~~~~~~~\x1b[m\x1b[K', "\x1b[01m\x1b[K./include/linux/mutex.h:87:22:\x1b[m\x1b[K \x1b[01;36m\x1b[Knote: \x1b[m\x1b[Kin definition of macro '\x1b[01m\x1b[KDEFINE_MUTEX\x1b[m\x1b[K'", '   87 |         struct mutex \x1b[01;36m\x1b[Kmutexname\x1b[m\x1b[K = __MUTEX_INITIALIZER(mutexname)', '      |                      \x1b[01;36m\x1b[K^~~~~~~~~\x1b[m\x1b[K', 'cc1: all warnings being treated as errors', 'make[4]: *** [scripts/Makefile.build:289: drivers/char/nvram.o] Error 1', 'make[4]: *** Waiting for unfinished jobs....', 'make[3]: *** [scripts/Makefile.build:548: drivers/char] Error 2', 'make[3]: *** Waiting for unfinished jobs....', 'make[2]: *** [scripts/Makefile.build:548: drivers] Error 2', 'make[2]: *** Waiting for unfinished jobs....', 'make[1]: *** [/home/linux_src/linux/Makefile:2141: .] Error 2', 'make: *** [Makefile:248: __sub-make] Error 2']

----------------------------------------------------------------------
Ran 1 test in 606.075s

FAILED (errors=1)

Is it a known issue ?

[vpuliyal]

@PraveenPenguin @abdhaleegit any idea about this issue ?

[vpuliyal]

@PraveenPenguin @abdhaleegit

I was able to successfully build the kernel after applying a workaround to remove the unused nvram_mutex definition from drivers/char/nvram.c. This avoids the -Werror=unused-variable failure during compilation.

sed -i '/nvram_mutex/d' drivers/char/nvram.c

Is it a best solution ?

[PraveenPenguin]

Please wait for this patch to be merged https://lore.kernel.org/lkml/20260428061540.73668-1-venkat88@linux.ibm.com/ , if you are block in your CI use case may have local fix what you have propesed

[vpuliyal]

@PraveenPenguin Thanks for the info.