[ast-bpf:kmalloc_nolock 6/7] mm/slub.c:3326:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false

[ast-bpf:kmalloc_nolock 6/7] mm/slub.c:3326:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false

[kernel test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git kmalloc_nolock
head:   de3de6fc810275dad0998ffed42d921690c667ec
commit: 8e58427a2c80d3a9be8b6f2f9ccc4319d1f27906 [6/7] slab: Introduce kmalloc_nolock() and kfree_nolock().
config: x86_64-buildonly-randconfig-004-20250718 (https://download.01.org/0day-ci/archive/20250718/202507181229.QStFKxIY-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250718/202507181229.QStFKxIY-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/202507181229.QStFKxIY-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> mm/slub.c:3326:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
    3326 |         local_lock_cpu_slab(s, flags);
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   mm/slub.c:3236:2: note: expanded from macro 'local_lock_cpu_slab'
    3236 |         lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/lockdep.h:279:15: note: expanded from macro 'lockdep_assert'
     279 |         do { WARN_ON(debug_locks && !(cond)); } while (0)
         |                      ^~~~~~~~~~~
   include/asm-generic/bug.h:123:25: note: expanded from macro 'WARN_ON'
     123 |         int __ret_warn_on = !!(condition);                              \
         |                                ^~~~~~~~~
   mm/slub.c:3351:27: note: uninitialized use occurs here
    3351 |         local_unlock_cpu_slab(s, flags);
         |                                  ^~~~~
   mm/slub.c:3240:48: note: expanded from macro 'local_unlock_cpu_slab'
    3240 |         local_unlock_irqrestore(&(s)->cpu_slab->lock, flags)
         |                                                       ^~~~~
   include/linux/local_lock.h:52:34: note: expanded from macro 'local_unlock_irqrestore'
      52 |         __local_unlock_irqrestore(lock, flags)
         |                                         ^~~~~
   include/linux/local_lock_internal.h:202:21: note: expanded from macro '__local_unlock_irqrestore'
     202 |                 local_irq_restore(flags);                       \
         |                                   ^~~~~
   include/linux/irqflags.h:240:61: note: expanded from macro 'local_irq_restore'
     240 | #define local_irq_restore(flags) do { raw_local_irq_restore(flags); } while (0)
         |                                                             ^~~~~
   include/linux/irqflags.h:179:26: note: expanded from macro 'raw_local_irq_restore'
     179 |                 arch_local_irq_restore(flags);          \
         |                                        ^~~~~
   mm/slub.c:3326:2: note: remove the '&&' if its condition is always true
    3326 |         local_lock_cpu_slab(s, flags);
         |         ^
   mm/slub.c:3236:2: note: expanded from macro 'local_lock_cpu_slab'
    3236 |         lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
         |         ^
   include/linux/lockdep.h:279:15: note: expanded from macro 'lockdep_assert'
     279 |         do { WARN_ON(debug_locks && !(cond)); } while (0)
         |                      ^
   mm/slub.c:3323:21: note: initialize the variable 'flags' to silence this warning
    3323 |         unsigned long flags;
         |                            ^
         |                             = 0
   1 warning generated.


vim +3326 mm/slub.c

  3312	
  3313	/*
  3314	 * Put a slab into a partial slab slot if available.
  3315	 *
  3316	 * If we did not find a slot then simply move all the partials to the
  3317	 * per node partial list.
  3318	 */
  3319	static void put_cpu_partial(struct kmem_cache *s, struct slab *slab, int drain)
  3320	{
  3321		struct slab *oldslab;
  3322		struct slab *slab_to_put = NULL;
  3323		unsigned long flags;
  3324		int slabs = 0;
  3325	
> 3326		local_lock_cpu_slab(s, flags);
  3327	
  3328		oldslab = this_cpu_read(s->cpu_slab->partial);
  3329	
  3330		if (oldslab) {
  3331			if (drain && oldslab->slabs >= s->cpu_partial_slabs) {
  3332				/*
  3333				 * Partial array is full. Move the existing set to the
  3334				 * per node partial list. Postpone the actual unfreezing
  3335				 * outside of the critical section.
  3336				 */
  3337				slab_to_put = oldslab;
  3338				oldslab = NULL;
  3339			} else {
  3340				slabs = oldslab->slabs;
  3341			}
  3342		}
  3343	
  3344		slabs++;
  3345	
  3346		slab->slabs = slabs;
  3347		slab->next = oldslab;
  3348	
  3349		this_cpu_write(s->cpu_slab->partial, slab);
  3350	
  3351		local_unlock_cpu_slab(s, flags);
  3352	
  3353		if (slab_to_put) {
  3354			__put_partials(s, slab_to_put);
  3355			stat(s, CPU_PARTIAL_DRAIN);
  3356		}
  3357	}
  3358	

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