diff mbox series

[1/1] mm/mmap_lock: Remove unnecessary 'NULL' values from Pointer

Message ID 20221008093942.3982-1-xupengfei@nfschina.com (mailing list archive)
State New
Headers show
Series [1/1] mm/mmap_lock: Remove unnecessary 'NULL' values from Pointer | expand

Commit Message

XU pengfei Oct. 8, 2022, 9:39 a.m. UTC 
Pointer variables allocate memory first, and then judge. There is no
need to initialize the assignment.

Signed-off-by: XU pengfei <xupengfei@nfschina.com>
---
 mm/mmap_lock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Miaohe Lin Oct. 8, 2022, 12:21 p.m. UTC | #1 
On 2022/10/8 17:39, XU pengfei wrote:
> Pointer variables allocate memory first, and then judge. There is no
> need to initialize the assignment.
> 
> Signed-off-by: XU pengfei <xupengfei@nfschina.com>
> ---
>  mm/mmap_lock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c
> index 1854850b4b89..65a57731aa15 100644
> --- a/mm/mmap_lock.c
> +++ b/mm/mmap_lock.c
> @@ -198,7 +198,7 @@ void trace_mmap_lock_unreg(void)
>   */
>  static const char *get_mm_memcg_path(struct mm_struct *mm)
>  {
> -	char *buf = NULL;
> +	char *buf;
>  	struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm);
>  
>  	if (memcg == NULL)

It seems if memcg == NULL, the code will go to out and return uninitialized @buf?

Thanks,
Miaohe Lin
kernel test robot Oct. 8, 2022, 1:14 p.m. UTC | #2 
Hi XU,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/XU-pengfei/mm-mmap_lock-Remove-unnecessary-NULL-values-from-Pointer/20221008-174149
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
config: x86_64-randconfig-a003-20221003
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
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/d8ed9ca4f5c0538ddfb42265c5f91cc185aa0507
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review XU-pengfei/mm-mmap_lock-Remove-unnecessary-NULL-values-from-Pointer/20221008-174149
        git checkout d8ed9ca4f5c0538ddfb42265c5f91cc185aa0507
        # 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=x86_64 SHELL=/bin/bash

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

All warnings (new ones prefixed by >>):

>> mm/mmap_lock.c:206:6: warning: variable 'buf' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
           if (unlikely(memcg->css.cgroup == NULL))
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/compiler.h:78:22: note: expanded from macro 'unlikely'
   # define unlikely(x)    __builtin_expect(!!(x), 0)
                           ^~~~~~~~~~~~~~~~~~~~~~~~~~
   mm/mmap_lock.c:218:9: note: uninitialized use occurs here
           return buf;
                  ^~~
   mm/mmap_lock.c:206:2: note: remove the 'if' if its condition is always false
           if (unlikely(memcg->css.cgroup == NULL))
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   mm/mmap_lock.c:204:6: warning: variable 'buf' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
           if (memcg == NULL)
               ^~~~~~~~~~~~~
   mm/mmap_lock.c:218:9: note: uninitialized use occurs here
           return buf;
                  ^~~
   mm/mmap_lock.c:204:2: note: remove the 'if' if its condition is always false
           if (memcg == NULL)
           ^~~~~~~~~~~~~~~~~~
   mm/mmap_lock.c:201:11: note: initialize the variable 'buf' to silence this warning
           char *buf;
                    ^
                     = NULL
   2 warnings generated.


vim +206 mm/mmap_lock.c

d01079f3d0c0a9 Mel Gorman     2021-06-30  184  
d01079f3d0c0a9 Mel Gorman     2021-06-30  185  #ifdef CONFIG_TRACING
d01079f3d0c0a9 Mel Gorman     2021-06-30  186  #ifdef CONFIG_MEMCG
2b5067a8143e34 Axel Rasmussen 2020-12-14  187  /*
2b5067a8143e34 Axel Rasmussen 2020-12-14  188   * Write the given mm_struct's memcg path to a percpu buffer, and return a
2b5067a8143e34 Axel Rasmussen 2020-12-14  189   * pointer to it. If the path cannot be determined, or no buffer was available
2b5067a8143e34 Axel Rasmussen 2020-12-14  190   * (because the trace event is being unregistered), NULL is returned.
2b5067a8143e34 Axel Rasmussen 2020-12-14  191   *
2b5067a8143e34 Axel Rasmussen 2020-12-14  192   * Note: buffers are allocated per-cpu to avoid locking, so preemption must be
2b5067a8143e34 Axel Rasmussen 2020-12-14  193   * disabled by the caller before calling us, and re-enabled only after the
2b5067a8143e34 Axel Rasmussen 2020-12-14  194   * caller is done with the pointer.
2b5067a8143e34 Axel Rasmussen 2020-12-14  195   *
2b5067a8143e34 Axel Rasmussen 2020-12-14  196   * The caller must call put_memcg_path_buf() once the buffer is no longer
2b5067a8143e34 Axel Rasmussen 2020-12-14  197   * needed. This must be done while preemption is still disabled.
2b5067a8143e34 Axel Rasmussen 2020-12-14  198   */
2b5067a8143e34 Axel Rasmussen 2020-12-14  199  static const char *get_mm_memcg_path(struct mm_struct *mm)
2b5067a8143e34 Axel Rasmussen 2020-12-14  200  {
d8ed9ca4f5c053 XU pengfei     2022-10-08  201  	char *buf;
2b5067a8143e34 Axel Rasmussen 2020-12-14  202  	struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm);
2b5067a8143e34 Axel Rasmussen 2020-12-14  203  
2b5067a8143e34 Axel Rasmussen 2020-12-14  204  	if (memcg == NULL)
2b5067a8143e34 Axel Rasmussen 2020-12-14  205  		goto out;
2b5067a8143e34 Axel Rasmussen 2020-12-14 @206  	if (unlikely(memcg->css.cgroup == NULL))
2b5067a8143e34 Axel Rasmussen 2020-12-14  207  		goto out_put;
2b5067a8143e34 Axel Rasmussen 2020-12-14  208  
2b5067a8143e34 Axel Rasmussen 2020-12-14  209  	buf = get_memcg_path_buf();
2b5067a8143e34 Axel Rasmussen 2020-12-14  210  	if (buf == NULL)
2b5067a8143e34 Axel Rasmussen 2020-12-14  211  		goto out_put;
2b5067a8143e34 Axel Rasmussen 2020-12-14  212  
2b5067a8143e34 Axel Rasmussen 2020-12-14  213  	cgroup_path(memcg->css.cgroup, buf, MEMCG_PATH_BUF_SIZE);
2b5067a8143e34 Axel Rasmussen 2020-12-14  214  
2b5067a8143e34 Axel Rasmussen 2020-12-14  215  out_put:
2b5067a8143e34 Axel Rasmussen 2020-12-14  216  	css_put(&memcg->css);
2b5067a8143e34 Axel Rasmussen 2020-12-14  217  out:
2b5067a8143e34 Axel Rasmussen 2020-12-14  218  	return buf;
2b5067a8143e34 Axel Rasmussen 2020-12-14  219  }
2b5067a8143e34 Axel Rasmussen 2020-12-14  220
diff mbox series

Patch

diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c
index 1854850b4b89..65a57731aa15 100644
--- a/mm/mmap_lock.c
+++ b/mm/mmap_lock.c
@@ -198,7 +198,7 @@  void trace_mmap_lock_unreg(void)
  */
 static const char *get_mm_memcg_path(struct mm_struct *mm)
 {
-	char *buf = NULL;
+	char *buf;
 	struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm);
 
 	if (memcg == NULL)