linux-kernel - Re: [PATCH v5 3/6] locking/rwsem: Disable preemption at all down_write*() and up

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Date:   Thu, 3 Nov 2022 20:00:53 -0400
From:   Waiman Long <longman@...hat.com>
To:     kernel test robot <lkp@...el.com>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>
Cc:     oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        john.p.donnelly@...cle.com, Hillf Danton <hdanton@...a.com>,
        Mukesh Ojha <quic_mojha@...cinc.com>,
        Ting11 Wang 王婷 <wangting11@...omi.com>
Subject: Re: [PATCH v5 3/6] locking/rwsem: Disable preemption at all
 down_write*() and up_write() code paths


On 11/3/22 16:04, kernel test robot wrote:
> Hi Waiman,
>
> I love your patch! Perhaps something to improve:
>
> [auto build test WARNING on tip/locking/core]
> [also build test WARNING on tip/master linus/master v6.1-rc3 next-20221103]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Waiman-Long/lockinig-rwsem-Fix-rwsem-bugs-enable-true-lock-handoff/20221104-023520
> patch link:    https://lore.kernel.org/r/20221103182936.217120-4-longman%40redhat.com
> patch subject: [PATCH v5 3/6] locking/rwsem: Disable preemption at all down_write*() and up_write() code paths
> config: m68k-allyesconfig
> compiler: m68k-linux-gcc (GCC) 12.1.0
> reproduce (this is a W=1 build):
>          wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>          chmod +x ~/bin/make.cross
>          # https://github.com/intel-lab-lkp/linux/commit/b83e7cdb918b02166fbe3954940a7bd6f04eef14
>          git remote add linux-review https://github.com/intel-lab-lkp/linux
>          git fetch --no-tags linux-review Waiman-Long/lockinig-rwsem-Fix-rwsem-bugs-enable-true-lock-handoff/20221104-023520
>          git checkout b83e7cdb918b02166fbe3954940a7bd6f04eef14
>          # save the config file
>          mkdir build_dir && cp config build_dir/.config
>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash kernel/locking/
>
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@...el.com>
>
> All warnings (new ones prefixed by >>):
>
>     kernel/locking/rwsem.c: In function '__down_write_common':
>>> kernel/locking/rwsem.c:1302:13: warning: variable 'ret' set but not used [-Wunused-but-set-variable]
>      1302 |         int ret = 0;
>           |             ^~~

Oh well, I will fix that.

Cheers,
Longman

>
> vim +/ret +1302 kernel/locking/rwsem.c
>
>    1296	
>    1297	/*
>    1298	 * lock for writing
>    1299	 */
>    1300	static inline int __down_write_common(struct rw_semaphore *sem, int state)
>    1301	{
>> 1302		int ret = 0;
>    1303	
>    1304		preempt_disable();
>    1305		if (unlikely(!rwsem_write_trylock(sem))) {
>    1306			if (IS_ERR(rwsem_down_write_slowpath(sem, state)))
>    1307				ret = -EINTR;
>    1308		}
>    1309		preempt_enable();
>    1310	
>    1311		return 0;
>    1312	}
>    1313	
>