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Date:   Wed, 2 Sep 2020 08:07:28 +0000
From:   "Xia, Hui" <hui.xia@...el.com>
To:     Leo Yan <leo.yan@...aro.org>, lkp <lkp@...el.com>
CC:     "kbuild-all@...ts.01.org" <kbuild-all@...ts.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>
Subject: RE: [kbuild-all] Re: include/asm-generic/qspinlock.h:94:9: sparse:
 sparse: context imbalance in '__msm_console_write' - unexpected unlock



>-----Original Message-----
>From: Leo Yan <leo.yan@...aro.org>
>Sent: 2020年8月31日 8:47
>To: lkp <lkp@...el.com>
>Cc: kbuild-all@...ts.01.org; linux-kernel@...r.kernel.org; Greg Kroah-Hartman
><gregkh@...uxfoundation.org>; Jeffrey Hugo <jeffrey.l.hugo@...il.com>
>Subject: [kbuild-all] Re: include/asm-generic/qspinlock.h:94:9: sparse: sparse:
>context imbalance in '__msm_console_write' - unexpected unlock
>
>Hi,
>
>On Sat, Aug 29, 2020 at 08:27:03AM +0800, kernel test robot wrote:
>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>> head:   005c53447a63cbce10de37406975a34d7bdc8704
>> commit: 0e4f7f920a5c6bfe5e851e989f27b35a0cc7fb7e tty: serial: msm_serial:
>Fix lockup for sysrq and oops
>> date:   9 months ago
>> config: arm64-randconfig-s031-20200829 (attached as .config)
>> compiler: aarch64-linux-gcc (GCC) 9.3.0
>> 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: v0.6.2-191-g10164920-dirty
>>         git checkout 0e4f7f920a5c6bfe5e851e989f27b35a0cc7fb7e
>>         # save the attached .config to linux build tree
>>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross
>> C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=arm64
>>
>> If you fix the issue, kindly add following tag as appropriate
>> Reported-by: kernel test robot <lkp@...el.com>
>>
>>
>> sparse warnings: (new ones prefixed by >>)
>>
>>    drivers/tty/serial/msm_serial.c:736:25: sparse: sparse: context imbalance in
>'msm_handle_rx_dm' - unexpected unlock
>>    drivers/tty/serial/msm_serial.c:802:28: sparse: sparse: context imbalance in
>'msm_handle_rx' - unexpected unlock
>>    drivers/tty/serial/msm_serial.c:1100:12: sparse: sparse: context imbalance in
>'msm_set_baud_rate' - unexpected unlock
>>    drivers/tty/serial/msm_serial.c: note: in included file (through
>arch/arm64/include/generated/asm/qspinlock.h,
>arch/arm64/include/asm/spinlock.h, include/linux/spinlock.h, ...):
>> >> include/asm-generic/qspinlock.h:94:9: sparse: sparse: context
>> >> imbalance in '__msm_console_write' - unexpected unlock
>
>I think this is a false positive report.  Let's see the locking relevant code in
>__msm_console_write():
Hi Yan,

Thanks for the clarification. Please ignore this report.
It was sent out unexpected. We will fix the robot bug soon.

Best Regards,
Hui
>
>  __msm_console_write() {
>
>      int locked = 1;
>
>      [...]
>
>      if (port->sysrq)
>          locked = 0;
>      else if (oops_in_progress)
>          locked = spin_trylock(&port->lock);
>      else
>          spin_lock(&port->lock);
>
>      [...]
>
>      if (locked)
>          spin_unlock(&port->lock);
>  }
>
>Since we need to handle oops and sysrq as special cases, it uses 'locked' to
>indicate the spinlock has been acquired and later will release spinlock if 'locked' is
>true.  So locking and unlocking are paired and I don't see what's the reason the
>robot reports the context imbalance.
>
>BTW, this report is not only for msm_serial driver, it also might be applied to
>many other serial drivers, e.g.
>
>  drivers/tty/serial/amba-pl011.c
>  drivers/tty/serial/xilinx_uartps.c
>  drivers/tty/serial/stm32-usart.c
>
>Maybe I miss something at here, if so please let me know.
>
>Thanks,
>Leo
>
>> #
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/com
>> mit/?id=0e4f7f920a5c6bfe5e851e989f27b35a0cc7fb7e
>> git remote add linus
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>> git fetch --no-tags linus master
>> git checkout 0e4f7f920a5c6bfe5e851e989f27b35a0cc7fb7e
>> vim +/__msm_console_write +94 include/asm-generic/qspinlock.h
>>
>> a33fda35e3a765 Waiman Long 2015-04-24  83
>> a33fda35e3a765 Waiman Long 2015-04-24  84  #ifndef queued_spin_unlock
>> a33fda35e3a765 Waiman Long 2015-04-24  85  /**
>> a33fda35e3a765 Waiman Long 2015-04-24  86   * queued_spin_unlock - release
>a queued spinlock
>> a33fda35e3a765 Waiman Long 2015-04-24  87   * @lock : Pointer to queued
>spinlock structure
>> a33fda35e3a765 Waiman Long 2015-04-24  88   */
>> a33fda35e3a765 Waiman Long 2015-04-24  89  static __always_inline void
>> queued_spin_unlock(struct qspinlock *lock)
>> a33fda35e3a765 Waiman Long 2015-04-24  90  {
>> a33fda35e3a765 Waiman Long 2015-04-24  91  	/*
>> ca50e426f96c90 Pan Xinhui  2016-06-03  92  	 * unlock() needs release
>semantics:
>> a33fda35e3a765 Waiman Long 2015-04-24  93  	 */
>> 626e5fbc143589 Will Deacon 2018-04-26 @94
>	smp_store_release(&lock->locked, 0);
>> a33fda35e3a765 Waiman Long 2015-04-24  95  }
>> a33fda35e3a765 Waiman Long 2015-04-24  96  #endif
>> a33fda35e3a765 Waiman Long 2015-04-24  97
>>
>> :::::: The code at line 94 was first introduced by commit
>> :::::: 626e5fbc14358901ddaa90ce510e0fbeab310432 locking/qspinlock: Use
>> smp_store_release() in queued_spin_unlock()
>>
>> :::::: TO: Will Deacon <will.deacon@....com>
>> :::::: CC: Ingo Molnar <mingo@...nel.org>
>>
>> ---
>> 0-DAY CI Kernel Test Service, Intel Corporation
>> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
>
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