Re: [PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[Tetsuo Handa]

Hello.

Thanks for doing build test, but I don't understand what is wrong.
As far as I can see, "struct percpu_rw_semaphore" contains "struct rw_semaphore"
and "struct rw_semaphore" contains "atomic_long_t count".
Then, why trying to read using atomic_long_read(&sem->rw_sem.count) causes

  note: expected 'const atomic_long_t * {aka const struct <anonymous> *}' but argument is of type '__s32 * {aka int *}'

warning? Is mips using different type?

struct percpu_rw_semaphore {
        struct rcu_sync         rss;
        unsigned int __percpu   *read_count;
        struct rw_semaphore     rw_sem; /* slowpath */
        struct rcuwait          writer; /* blocked writer */
        int                     readers_block;
};

/* All arch specific implementations share the same struct */
struct rw_semaphore {
        atomic_long_t count;
        struct list_head wait_list;
        raw_spinlock_t wait_lock;
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
        struct optimistic_spin_queue osq; /* spinner MCS lock */
        /*
         * Write owner. Used as a speculative check to see
         * if the owner is running on the cpu.
         */
        struct task_struct *owner;
#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC
        struct lockdep_map      dep_map;
#endif
};

On 2018/07/07 20:31, kbuild test robot wrote:
> Hi Tetsuo,
> 
> I love your patch! Yet something to improve:
> 
> [auto build test ERROR on next-20180706]
> [also build test ERROR on v4.18-rc3]
> [cannot apply to tip/auto-latest tip/sched/core linus/master v4.18-rc3 v4.18-rc2 v4.18-rc1]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> 
> url:    https://github.com/0day-ci/linux/commits/Tetsuo-Handa/locking-lockdep-Dump-state-of-percpu_rwsem-upon-hung-up/20180707-143406
> config: mips-allmodconfig (attached as .config)
> compiler: mips-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         GCC_VERSION=7.2.0 make.cross ARCH=mips 
> 
> All error/warnings (new ones prefixed by >>):
> 
>    In file included from include/linux/kernel.h:14:0,
>                     from include/asm-generic/bug.h:18,
>                     from arch/mips/include/asm/bug.h:42,
>                     from include/linux/bug.h:5,
>                     from include/linux/mmdebug.h:5,
>                     from include/linux/mm.h:9,
>                     from kernel/hung_task.c:8:
>    kernel/hung_task.c: In function 'dump_percpu_rwsem_state':
>>> kernel/hung_task.c:95:20: error: passing argument 1 of 'atomic_long_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
>       atomic_long_read(&sem->rw_sem.count));
>                        ^
>    include/linux/printk.h:311:34: note: in definition of macro 'pr_info'
>      printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
>                                      ^~~~~~~~~~~
>    In file included from include/linux/atomic.h:1309:0,
>                     from arch/mips/include/asm/processor.h:14,
>                     from arch/mips/include/asm/thread_info.h:16,
>                     from include/linux/thread_info.h:38,
>                     from include/asm-generic/preempt.h:5,
>                     from ./arch/mips/include/generated/asm/preempt.h:1,
>                     from include/linux/preempt.h:81,
>                     from include/linux/spinlock.h:51,
>                     from include/linux/mmzone.h:8,
>                     from include/linux/gfp.h:6,
>                     from include/linux/mm.h:10,
>                     from kernel/hung_task.c:8:
>    include/asm-generic/atomic-long.h:41:20: note: expected 'const atomic_long_t * {aka const struct <anonymous> *}' but argument is of type '__s32 * {aka int *}'
>     static inline long atomic_long_read##mo(const atomic_long_t *l)  \
>                        ^
>>> include/asm-generic/atomic-long.h:47:1: note: in expansion of macro 'ATOMIC_LONG_READ_OP'
>     ATOMIC_LONG_READ_OP()
>     ^~~~~~~~~~~~~~~~~~~
>    cc1: some warnings being treated as errors