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* [tip:locking/urgent 3/5] kernel/futex.c:2016:18: warning: variable 'vpid' set but not used
@ 2021-09-02 22:06 kernel test robot
  0 siblings, 0 replies; only message in thread
From: kernel test robot @ 2021-09-02 22:06 UTC (permalink / raw)
  To: Thomas Gleixner; +Cc: kbuild-all, linux-kernel, x86

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git locking/urgent
head:   340576590dac4bb58d532a8ad5bfa806d8ab473c
commit: 4f07ec0d76f242d4ca0f0c0c6f7293c28254a554 [3/5] futex: Prevent inconsistent state and exit race
config: riscv-randconfig-r042-20210903 (attached as .config)
compiler: riscv64-linux-gcc (GCC) 11.2.0
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://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=4f07ec0d76f242d4ca0f0c0c6f7293c28254a554
        git remote add tip https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
        git fetch --no-tags tip locking/urgent
        git checkout 4f07ec0d76f242d4ca0f0c0c6f7293c28254a554
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross ARCH=riscv 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   kernel/futex.c: In function 'futex_proxy_trylock_atomic':
>> kernel/futex.c:2016:18: warning: variable 'vpid' set but not used [-Wunused-but-set-variable]
    2016 |         int ret, vpid;
         |                  ^~~~


vim +/vpid +2016 kernel/futex.c

52400ba946759af Darren Hart           2009-04-03  1981  
52400ba946759af Darren Hart           2009-04-03  1982  /**
52400ba946759af Darren Hart           2009-04-03  1983   * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
52400ba946759af Darren Hart           2009-04-03  1984   * @pifutex:		the user address of the to futex
52400ba946759af Darren Hart           2009-04-03  1985   * @hb1:		the from futex hash bucket, must be locked by the caller
52400ba946759af Darren Hart           2009-04-03  1986   * @hb2:		the to futex hash bucket, must be locked by the caller
52400ba946759af Darren Hart           2009-04-03  1987   * @key1:		the from futex key
52400ba946759af Darren Hart           2009-04-03  1988   * @key2:		the to futex key
bab5bc9e8576388 Darren Hart           2009-04-07  1989   * @ps:			address to store the pi_state pointer
3ef240eaff36b81 Thomas Gleixner       2019-11-06  1990   * @exiting:		Pointer to store the task pointer of the owner task
3ef240eaff36b81 Thomas Gleixner       2019-11-06  1991   *			which is in the middle of exiting
bab5bc9e8576388 Darren Hart           2009-04-07  1992   * @set_waiters:	force setting the FUTEX_WAITERS bit (1) or not (0)
52400ba946759af Darren Hart           2009-04-03  1993   *
52400ba946759af Darren Hart           2009-04-03  1994   * Try and get the lock on behalf of the top waiter if we can do it atomically.
bab5bc9e8576388 Darren Hart           2009-04-07  1995   * Wake the top waiter if we succeed.  If the caller specified set_waiters,
bab5bc9e8576388 Darren Hart           2009-04-07  1996   * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
bab5bc9e8576388 Darren Hart           2009-04-07  1997   * hb1 and hb2 must be held by the caller.
52400ba946759af Darren Hart           2009-04-03  1998   *
3ef240eaff36b81 Thomas Gleixner       2019-11-06  1999   * @exiting is only set when the return value is -EBUSY. If so, this holds
3ef240eaff36b81 Thomas Gleixner       2019-11-06  2000   * a refcount on the exiting task on return and the caller needs to drop it
3ef240eaff36b81 Thomas Gleixner       2019-11-06  2001   * after waiting for the exit to complete.
3ef240eaff36b81 Thomas Gleixner       2019-11-06  2002   *
6c23cbbd5056b15 Randy Dunlap          2013-03-05  2003   * Return:
7b4ff1adb57ad96 Mauro Carvalho Chehab 2017-05-11  2004   *  -  0 - failed to acquire the lock atomically;
7b4ff1adb57ad96 Mauro Carvalho Chehab 2017-05-11  2005   *  - >0 - acquired the lock, return value is vpid of the top_waiter
7b4ff1adb57ad96 Mauro Carvalho Chehab 2017-05-11  2006   *  - <0 - error
52400ba946759af Darren Hart           2009-04-03  2007   */
3ef240eaff36b81 Thomas Gleixner       2019-11-06  2008  static int
3ef240eaff36b81 Thomas Gleixner       2019-11-06  2009  futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
3ef240eaff36b81 Thomas Gleixner       2019-11-06  2010  			   struct futex_hash_bucket *hb2, union futex_key *key1,
3ef240eaff36b81 Thomas Gleixner       2019-11-06  2011  			   union futex_key *key2, struct futex_pi_state **ps,
3ef240eaff36b81 Thomas Gleixner       2019-11-06  2012  			   struct task_struct **exiting, int set_waiters)
52400ba946759af Darren Hart           2009-04-03  2013  {
bab5bc9e8576388 Darren Hart           2009-04-07  2014  	struct futex_q *top_waiter = NULL;
52400ba946759af Darren Hart           2009-04-03  2015  	u32 curval;
866293ee5422758 Thomas Gleixner       2014-05-12 @2016  	int ret, vpid;
52400ba946759af Darren Hart           2009-04-03  2017  
52400ba946759af Darren Hart           2009-04-03  2018  	if (get_futex_value_locked(&curval, pifutex))
52400ba946759af Darren Hart           2009-04-03  2019  		return -EFAULT;
52400ba946759af Darren Hart           2009-04-03  2020  
ab51fbab39d864f Davidlohr Bueso       2015-06-29  2021  	if (unlikely(should_fail_futex(true)))
ab51fbab39d864f Davidlohr Bueso       2015-06-29  2022  		return -EFAULT;
ab51fbab39d864f Davidlohr Bueso       2015-06-29  2023  
bab5bc9e8576388 Darren Hart           2009-04-07  2024  	/*
bab5bc9e8576388 Darren Hart           2009-04-07  2025  	 * Find the top_waiter and determine if there are additional waiters.
bab5bc9e8576388 Darren Hart           2009-04-07  2026  	 * If the caller intends to requeue more than 1 waiter to pifutex,
bab5bc9e8576388 Darren Hart           2009-04-07  2027  	 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
bab5bc9e8576388 Darren Hart           2009-04-07  2028  	 * as we have means to handle the possible fault.  If not, don't set
93d0955e6cf562d Ingo Molnar           2021-05-12  2029  	 * the bit unnecessarily as it will force the subsequent unlock to enter
bab5bc9e8576388 Darren Hart           2009-04-07  2030  	 * the kernel.
bab5bc9e8576388 Darren Hart           2009-04-07  2031  	 */
52400ba946759af Darren Hart           2009-04-03  2032  	top_waiter = futex_top_waiter(hb1, key1);
52400ba946759af Darren Hart           2009-04-03  2033  
52400ba946759af Darren Hart           2009-04-03  2034  	/* There are no waiters, nothing for us to do. */
52400ba946759af Darren Hart           2009-04-03  2035  	if (!top_waiter)
52400ba946759af Darren Hart           2009-04-03  2036  		return 0;
52400ba946759af Darren Hart           2009-04-03  2037  
dc7109aaa233d83 Thomas Gleixner       2021-08-15  2038  	/*
dc7109aaa233d83 Thomas Gleixner       2021-08-15  2039  	 * Ensure that this is a waiter sitting in futex_wait_requeue_pi()
dc7109aaa233d83 Thomas Gleixner       2021-08-15  2040  	 * and waiting on the 'waitqueue' futex which is always !PI.
dc7109aaa233d83 Thomas Gleixner       2021-08-15  2041  	 */
dc7109aaa233d83 Thomas Gleixner       2021-08-15  2042  	if (!top_waiter->rt_waiter || top_waiter->pi_state)
a974b54036f79dd Colin Ian King        2021-08-18  2043  		return -EINVAL;
dc7109aaa233d83 Thomas Gleixner       2021-08-15  2044  
84bc4af59081ee9 Darren Hart           2009-08-13  2045  	/* Ensure we requeue to the expected futex. */
84bc4af59081ee9 Darren Hart           2009-08-13  2046  	if (!match_futex(top_waiter->requeue_pi_key, key2))
84bc4af59081ee9 Darren Hart           2009-08-13  2047  		return -EINVAL;
84bc4af59081ee9 Darren Hart           2009-08-13  2048  
07d91ef510fb16a Thomas Gleixner       2021-08-15  2049  	/* Ensure that this does not race against an early wakeup */
07d91ef510fb16a Thomas Gleixner       2021-08-15  2050  	if (!futex_requeue_pi_prepare(top_waiter, NULL))
07d91ef510fb16a Thomas Gleixner       2021-08-15  2051  		return -EAGAIN;
07d91ef510fb16a Thomas Gleixner       2021-08-15  2052  
^1da177e4c3f415 Linus Torvalds        2005-04-16  2053  	/*
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2054  	 * Try to take the lock for top_waiter and set the FUTEX_WAITERS bit
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2055  	 * in the contended case or if @set_waiters is true.
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2056  	 *
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2057  	 * In the contended case PI state is attached to the lock owner. If
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2058  	 * the user space lock can be acquired then PI state is attached to
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2059  	 * the new owner (@top_waiter->task) when @set_waiters is true.
52400ba946759af Darren Hart           2009-04-03  2060  	 */
866293ee5422758 Thomas Gleixner       2014-05-12  2061  	vpid = task_pid_vnr(top_waiter->task);
bab5bc9e8576388 Darren Hart           2009-04-07  2062  	ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
3ef240eaff36b81 Thomas Gleixner       2019-11-06  2063  				   exiting, set_waiters);
866293ee5422758 Thomas Gleixner       2014-05-12  2064  	if (ret == 1) {
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2065  		/*
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2066  		 * Lock was acquired in user space and PI state was
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2067  		 * attached to @top_waiter->task. That means state is fully
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2068  		 * consistent and the waiter can return to user space
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2069  		 * immediately after the wakeup.
4f07ec0d76f242d Thomas Gleixner       2021-09-02  2070  		 */
beda2c7ea2c15ed Darren Hart           2009-08-09  2071  		requeue_pi_wake_futex(top_waiter, key2, hb2);
07d91ef510fb16a Thomas Gleixner       2021-08-15  2072  	} else if (ret < 0) {
07d91ef510fb16a Thomas Gleixner       2021-08-15  2073  		/* Rewind top_waiter::requeue_state */
07d91ef510fb16a Thomas Gleixner       2021-08-15  2074  		futex_requeue_pi_complete(top_waiter, ret);
07d91ef510fb16a Thomas Gleixner       2021-08-15  2075  	} else {
07d91ef510fb16a Thomas Gleixner       2021-08-15  2076  		/*
07d91ef510fb16a Thomas Gleixner       2021-08-15  2077  		 * futex_lock_pi_atomic() did not acquire the user space
07d91ef510fb16a Thomas Gleixner       2021-08-15  2078  		 * futex, but managed to establish the proxy lock and pi
07d91ef510fb16a Thomas Gleixner       2021-08-15  2079  		 * state. top_waiter::requeue_state cannot be fixed up here
07d91ef510fb16a Thomas Gleixner       2021-08-15  2080  		 * because the waiter is not enqueued on the rtmutex
07d91ef510fb16a Thomas Gleixner       2021-08-15  2081  		 * yet. This is handled at the callsite depending on the
07d91ef510fb16a Thomas Gleixner       2021-08-15  2082  		 * result of rt_mutex_start_proxy_lock() which is
07d91ef510fb16a Thomas Gleixner       2021-08-15  2083  		 * guaranteed to be reached with this function returning 0.
07d91ef510fb16a Thomas Gleixner       2021-08-15  2084  		 */
866293ee5422758 Thomas Gleixner       2014-05-12  2085  	}
52400ba946759af Darren Hart           2009-04-03  2086  	return ret;
52400ba946759af Darren Hart           2009-04-03  2087  }
52400ba946759af Darren Hart           2009-04-03  2088  

:::::: The code at line 2016 was first introduced by commit
:::::: 866293ee54227584ffcb4a42f69c1f365974ba7f futex: Add another early deadlock detection check

:::::: TO: Thomas Gleixner <tglx@linutronix.de>
:::::: CC: Thomas Gleixner <tglx@linutronix.de>

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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