Re: [PATCH 1/4] mm/swap, memcg: Introduce infrastructure for cgroup-based swap priority

[YoungJun Park <youngjun.park@lge.com>]

On Thu, Jul 17, 2025 at 07:20:58PM +0800, kernel test robot wrote:
> Hi Youngjun,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on 347e9f5043c89695b01e66b3ed111755afcf1911]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Youngjun-Park/mm-swap-memcg-Introduce-infrastructure-for-cgroup-based-swap-priority/20250717-042648
> base:   347e9f5043c89695b01e66b3ed111755afcf1911
> patch link:    https://lore.kernel.org/r/20250716202006.3640584-2-youngjun.park%40lge.com
> patch subject: [PATCH 1/4] mm/swap, memcg: Introduce infrastructure for cgroup-based swap priority
> config: loongarch-allyesconfig (https://download.01.org/0day-ci/archive/20250717/202507171936.fGW4muEc-lkp@intel.com/config)
> compiler: clang version 21.0.0git (https://github.com/llvm/llvm-project 16534d19bf50bde879a83f0ae62875e2c5120e64)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250717/202507171936.fGW4muEc-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202507171936.fGW4muEc-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
> >> mm/memcontrol.c:5462:12: warning: variable 'id' is uninitialized when used here [-Wuninitialized]
>     5462 |                                 memcg, id, SWAP_PRIORITY_GLOBAL);
>          |                                        ^~
>    mm/memcontrol.c:5414:8: note: initialize the variable 'id' to silence this warning
>     5414 |         u64 id;
>          |               ^
>          |                = 0
>    1 warning generated.
> 
> 
> vim +/id +5462 mm/memcontrol.c
> 
>   5408	
>   5409	#ifdef CONFIG_SWAP_CGROUP_PRIORITY
>   5410	static ssize_t swap_cgroup_priority_write(struct kernfs_open_file *of,
>   5411						  char *buf, size_t nbytes, loff_t off)
>   5412	{
>   5413		struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
>   5414		u64 id;
>   5415		int prio;
>   5416		int ret;
>   5417		char first_token[32];
>   5418		char second_token[32];
>   5419		char dummy[2];
>   5420		char *stripped_buf;
>   5421		int num_parsed;
>   5422	
>   5423		stripped_buf = strstrip(buf);
>   5424		num_parsed = sscanf(stripped_buf, "%31s %31s %1s", first_token,
>   5425				    second_token, dummy);
>   5426		if (num_parsed == 2) {
>   5427			if (strcmp(first_token, "default") == 0) {
>   5428				if (strcmp(second_token, "none") == 0)
>   5429					ret = apply_swap_cgroup_priority(
>   5430						memcg, DEFAULT_ID, SWAP_PRIORITY_GLOBAL);
>   5431				else if (strcmp(second_token, "disabled") == 0)
>   5432					ret = apply_swap_cgroup_priority(
>   5433						memcg, DEFAULT_ID, SWAP_PRIORITY_DISABLE);
>   5434				else
>   5435					ret = -EINVAL;
>   5436			} else {
>   5437				ret = kstrtoull(first_token, 10, &id);
>   5438				if (ret)
>   5439					return -EINVAL;
>   5440	
>   5441				if (strcmp(second_token, "none") == 0) {
>   5442					ret = apply_swap_cgroup_priority(
>   5443						memcg, id, SWAP_PRIORITY_GLOBAL);
>   5444				} else if (strcmp(second_token, "disabled") == 0) {
>   5445					ret = apply_swap_cgroup_priority(
>   5446						memcg, id, SWAP_PRIORITY_DISABLE);
>   5447				} else {
>   5448					ret = kstrtoint(second_token, 10, &prio);
>   5449					if (ret)
>   5450						return -EINVAL;
>   5451					if (prio == -1)
>   5452						return -EINVAL;
>   5453					else if (prio > SHRT_MAX || prio < SHRT_MIN)
>   5454						return -EINVAL;
>   5455					ret = apply_swap_cgroup_priority(memcg, id,
>   5456									 prio);
>   5457				}
>   5458			}
>   5459		} else if (num_parsed == 1) {
>   5460			if (strcmp(first_token, "none") == 0)
>   5461				ret = apply_swap_cgroup_priority(
> > 5462					memcg, id, SWAP_PRIORITY_GLOBAL);
>   5463			else if (strcmp(first_token, "disabled") == 0)
>   5464				ret = apply_swap_cgroup_priority(
>   5465					memcg, id, SWAP_PRIORITY_DISABLE);
>   5466			else
>   5467				ret = -EINVAL;
>   5468		} else {
>   5469			return -EINVAL;
>   5470		}
>   5471	
>   5472		if (ret)
>   5473			return ret;
>   5474	
>   5475		return nbytes;
>   5476	}
>   5477	

This is an initialization bug where the "default" value may not be handled
correctly in certain cases, such as:

  e.g. echo none > memory.swap.priority

I should have checked this more carefully. I will fix the issue and add
a test case in the next patch revision.

Best regards,
Youngjun Park