Re: [PATCH 3/3] mm/slub: Fix potential deadlock problem in slab_attr_store()

[kbuild test robot <lkp@intel.com>]

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Hi Waiman,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on tip/locking/core]
[also build test ERROR on tip/auto-latest linus/master v5.6-rc1 next-20200213]
[cannot apply to arm-perf/for-next/perf]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Waiman-Long/locking-mutex-Add-mutex_timed_lock-to-solve-potential-deadlock-problems/20200213-063401
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 41f0e29190ac9e38099a37abd1a8a4cb1dc21233
config: x86_64-randconfig-s2-20200213 (attached as .config)
compiler: gcc-6 (Debian 6.3.0-18+deb9u1) 6.3.0 20170516
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

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

All errors (new ones prefixed by >>):

   mm/slub.c: In function 'slab_attr_store':
>> mm/slub.c:5542:7: error: implicit declaration of function 'mutex_timed_lock' [-Werror=implicit-function-declaration]
      if (mutex_timed_lock(&slab_mutex, 100) < 0)
          ^~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/mutex_timed_lock +5542 mm/slub.c

  5519	
  5520	static ssize_t slab_attr_store(struct kobject *kobj,
  5521					struct attribute *attr,
  5522					const char *buf, size_t len)
  5523	{
  5524		struct slab_attribute *attribute;
  5525		struct kmem_cache *s;
  5526		int err;
  5527	
  5528		attribute = to_slab_attr(attr);
  5529		s = to_slab(kobj);
  5530	
  5531		if (!attribute->store)
  5532			return -EIO;
  5533	
  5534		err = attribute->store(s, buf, len);
  5535	#ifdef CONFIG_MEMCG
  5536		if (slab_state >= FULL && err >= 0 && is_root_cache(s)) {
  5537			struct kmem_cache *c;
  5538	
  5539			/*
  5540			 * Timeout after 100ms
  5541			 */
> 5542			if (mutex_timed_lock(&slab_mutex, 100) < 0)
  5543				return -EBUSY;
  5544	
  5545			if (s->max_attr_size < len)
  5546				s->max_attr_size = len;
  5547	
  5548			/*
  5549			 * This is a best effort propagation, so this function's return
  5550			 * value will be determined by the parent cache only. This is
  5551			 * basically because not all attributes will have a well
  5552			 * defined semantics for rollbacks - most of the actions will
  5553			 * have permanent effects.
  5554			 *
  5555			 * Returning the error value of any of the children that fail
  5556			 * is not 100 % defined, in the sense that users seeing the
  5557			 * error code won't be able to know anything about the state of
  5558			 * the cache.
  5559			 *
  5560			 * Only returning the error code for the parent cache at least
  5561			 * has well defined semantics. The cache being written to
  5562			 * directly either failed or succeeded, in which case we loop
  5563			 * through the descendants with best-effort propagation.
  5564			 */
  5565			for_each_memcg_cache(c, s)
  5566				attribute->store(c, buf, len);
  5567			mutex_unlock(&slab_mutex);
  5568		}
  5569	#endif
  5570		return err;
  5571	}
  5572	

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

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