linux-kernel - Re: [PATCH v2 06/12] locking/qspinlock: merge qspinlock

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Date:   Thu, 14 Jul 2022 22:16:31 +0800
From:   kernel test robot <lkp@...el.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        Nicholas Piggin <npiggin@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "linux-kernel @ vger . kernel . org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 06/12] locking/qspinlock: merge qspinlock_paravirt.h
 into qspinlock.c

Hi Nicholas,

I love your patch! Perhaps something to improve:

[auto build test WARNING on tip/locking/core]
[also build test WARNING on tip/x86/core powerpc/next linus/master v5.19-rc6 next-20220714]
[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/Nicholas-Piggin/locking-qspinlock-simplify-code-generation/20220713-151009
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git eae6d58d67d9739be5f7ae2dbead1d0ef6528243
config: i386-randconfig-a004
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project 5e61b9c556267086ef9b743a0b57df302eef831b)
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/91668ee1ed703d7ea84e314136dc732da05ec9e7
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Nicholas-Piggin/locking-qspinlock-simplify-code-generation/20220713-151009
        git checkout 91668ee1ed703d7ea84e314136dc732da05ec9e7
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 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 >>):

   In file included from kernel/locking/qspinlock.c:29:
   kernel/locking/qspinlock_stat.h:36:9: warning: no previous prototype for function 'lockevent_read' [-Wmissing-prototypes]
   ssize_t lockevent_read(struct file *file, char __user *user_buf,
           ^
   kernel/locking/qspinlock_stat.h:36:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   ssize_t lockevent_read(struct file *file, char __user *user_buf,
   ^
   static 
>> kernel/locking/qspinlock.c:705:1: warning: no previous prototype for function '__pv_queued_spin_unlock_slowpath' [-Wmissing-prototypes]
   __pv_queued_spin_unlock_slowpath(struct qspinlock *lock, u8 locked)
   ^
   kernel/locking/qspinlock.c:704:11: note: declare 'static' if the function is not intended to be used outside of this translation unit
   __visible void
             ^
             static 
   2 warnings generated.


vim +/__pv_queued_spin_unlock_slowpath +705 kernel/locking/qspinlock.c

   699	
   700	/*
   701	 * PV versions of the unlock fastpath and slowpath functions to be used
   702	 * instead of queued_spin_unlock().
   703	 */
   704	__visible void
 > 705	__pv_queued_spin_unlock_slowpath(struct qspinlock *lock, u8 locked)
   706	{
   707		struct qnode *node;
   708	
   709		if (unlikely(locked != _Q_SLOW_VAL)) {
   710			WARN(!debug_locks_silent,
   711			     "pvqspinlock: lock 0x%lx has corrupted value 0x%x!\n",
   712			     (unsigned long)lock, atomic_read(&lock->val));
   713			return;
   714		}
   715	
   716		/*
   717		 * A failed cmpxchg doesn't provide any memory-ordering guarantees,
   718		 * so we need a barrier to order the read of the node data in
   719		 * pv_unhash *after* we've read the lock being _Q_SLOW_VAL.
   720		 *
   721		 * Matches the cmpxchg() in pv_wait_head_or_lock() setting _Q_SLOW_VAL.
   722		 */
   723		smp_rmb();
   724	
   725		/*
   726		 * Since the above failed to release, this must be the SLOW path.
   727		 * Therefore start by looking up the blocked node and unhashing it.
   728		 */
   729		node = pv_unhash(lock);
   730	
   731		/*
   732		 * Now that we have a reference to the (likely) blocked qnode,
   733		 * release the lock.
   734		 */
   735		smp_store_release(&lock->locked, 0);
   736	
   737		/*
   738		 * At this point the memory pointed at by lock can be freed/reused,
   739		 * however we can still use the qnode to kick the CPU.
   740		 * The other vCPU may not really be halted, but kicking an active
   741		 * vCPU is harmless other than the additional latency in completing
   742		 * the unlock.
   743		 */
   744		lockevent_inc(pv_kick_unlock);
   745		pv_kick(node->cpu);
   746	}
   747	

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

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