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