linux-kernel - Re: Re: Crash with PREEMPT

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Date:   Tue, 29 Nov 2022 13:26:36 +0800
From:   kernel test robot <lkp@...el.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Will Deacon <will@...nel.org>, Jan Kara <jack@...e.cz>
Cc:     oe-kbuild-all@...ts.linux.dev, Waiman Long <longman@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: Re: Crash with PREEMPT_RT on aarch64 machine

Hi Sebastian,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on tip/locking/core]
[also build test WARNING on linus/master v6.1-rc7 next-20221128]
[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/Sebastian-Andrzej-Siewior/Re-Crash-with-PREEMPT_RT-on-aarch64-machine/20221129-000000
patch link:    https://lore.kernel.org/r/Y4Tapja2qq8HiHBZ%40linutronix.de
patch subject: Re: Crash with PREEMPT_RT on aarch64 machine
config: microblaze-randconfig-s041-20221128
compiler: microblaze-linux-gcc (GCC) 12.1.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # apt-get install sparse
        # sparse version: v0.6.4-39-gce1a6720-dirty
        # https://github.com/intel-lab-lkp/linux/commit/d4aea399f0b5472dc15a4c623d99b4ae79005050
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Sebastian-Andrzej-Siewior/Re-Crash-with-PREEMPT_RT-on-aarch64-machine/20221129-000000
        git checkout d4aea399f0b5472dc15a4c623d99b4ae79005050
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=microblaze SHELL=/bin/bash kernel/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>

sparse warnings: (new ones prefixed by >>)
   kernel/locking/rtmutex_api.c: note: in included file:
>> kernel/locking/rtmutex.c:100:9: sparse: sparse: incompatible types for operation (!=):
>> kernel/locking/rtmutex.c:100:9: sparse:    struct task_struct *
>> kernel/locking/rtmutex.c:100:9: sparse:    unsigned long

vim +100 kernel/locking/rtmutex.c

    64	
    65	/*
    66	 * lock->owner state tracking:
    67	 *
    68	 * lock->owner holds the task_struct pointer of the owner. Bit 0
    69	 * is used to keep track of the "lock has waiters" state.
    70	 *
    71	 * owner	bit0
    72	 * NULL		0	lock is free (fast acquire possible)
    73	 * NULL		1	lock is free and has waiters and the top waiter
    74	 *				is going to take the lock*
    75	 * taskpointer	0	lock is held (fast release possible)
    76	 * taskpointer	1	lock is held and has waiters**
    77	 *
    78	 * The fast atomic compare exchange based acquire and release is only
    79	 * possible when bit 0 of lock->owner is 0.
    80	 *
    81	 * (*) It also can be a transitional state when grabbing the lock
    82	 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
    83	 * we need to set the bit0 before looking at the lock, and the owner may be
    84	 * NULL in this small time, hence this can be a transitional state.
    85	 *
    86	 * (**) There is a small time when bit 0 is set but there are no
    87	 * waiters. This can happen when grabbing the lock in the slow path.
    88	 * To prevent a cmpxchg of the owner releasing the lock, we need to
    89	 * set this bit before looking at the lock.
    90	 */
    91	
    92	static __always_inline void
    93	rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner)
    94	{
    95		unsigned long val = (unsigned long)owner;
    96	
    97		if (rt_mutex_has_waiters(lock))
    98			val |= RT_MUTEX_HAS_WAITERS;
    99	
 > 100		WARN_ON_ONCE(cmpxchg_acquire(&lock->owner, RT_MUTEX_HAS_WAITERS, val) != RT_MUTEX_HAS_WAITERS);
   101	}
   102	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

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