Pointer variables allocate memory first, and then judge. There is no
need to initialize the assignment.
Signed-off-by: XU pengfei <[email protected]>
---
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)
--
2.18.2
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 <[email protected]>
> ---
> 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
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 <[email protected]>
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
--
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https://01.org/lkp