[android-common:android16-6.12 0/1] mm/slub.c:775:31: sparse: sparse: unsigned value that used to be signed checked against zero?

:::::: 
:::::: Manual check reason: "low confidence static check warning: mm/slub.c:775:31: sparse: sparse: unsigned value that used to be signed checked against zero?"
:::::: 

BCC: [email protected]
CC: [email protected]
TO: [email protected]

Hi Harry,

FYI, the error/warning was bisected to this commit, please ignore it if it's irrelevant.

tree:   https://android.googlesource.com/kernel/common android16-6.12
head:   749a6f9d41aa0bad1b1893ebae8598ca7875d09e
commit: b6e5cef4d6df31f7e61f2e2713b3358a0b48f7e7 [0/1] mm/slab: use unsigned long for orig_size to ensure proper metadata align
:::::: branch date: 2 days ago
:::::: commit date: 5 months ago
config: x86_64-randconfig-122-20260808 (https://download.01.org/0day-ci/archive/20260808/[email protected]/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
sparse: v0.6.5-rc1
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260808/[email protected]/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 <[email protected]>
| Closes: https://lore.kernel.org/r/[email protected]/

sparse warnings: (new ones prefixed by >>)
>> mm/slub.c:775:31: sparse: sparse: unsigned value that used to be signed checked against zero?
   mm/slub.c:1616:34: sparse: signed value source
   mm/slub.c:3179:55: sparse: sparse: context imbalance in '__put_partials' - unexpected unlock
   mm/slub.c:4475:47: sparse: sparse: context imbalance in '__slab_free' - unexpected unlock

vim +775 mm/slub.c

b789ef518b2a72 Christoph Lameter 2011-06-01  752  
59090e479ac78a Peng Fan          2024-08-29  753  /*
59090e479ac78a Peng Fan          2024-08-29  754   * kmalloc caches has fixed sizes (mostly power of 2), and kmalloc() API
59090e479ac78a Peng Fan          2024-08-29  755   * family will round up the real request size to these fixed ones, so
59090e479ac78a Peng Fan          2024-08-29  756   * there could be an extra area than what is requested. Save the original
59090e479ac78a Peng Fan          2024-08-29  757   * request size in the meta data area, for better debug and sanity check.
59090e479ac78a Peng Fan          2024-08-29  758   */
59090e479ac78a Peng Fan          2024-08-29  759  static inline void set_orig_size(struct kmem_cache *s,
b6e5cef4d6df31 Harry Yoo         2026-01-13  760  				void *object, unsigned long orig_size)
59090e479ac78a Peng Fan          2024-08-29  761  {
59090e479ac78a Peng Fan          2024-08-29  762  	void *p = kasan_reset_tag(object);
59090e479ac78a Peng Fan          2024-08-29  763  	unsigned int kasan_meta_size;
59090e479ac78a Peng Fan          2024-08-29  764  
59090e479ac78a Peng Fan          2024-08-29  765  	if (!slub_debug_orig_size(s))
59090e479ac78a Peng Fan          2024-08-29  766  		return;
59090e479ac78a Peng Fan          2024-08-29  767  
59090e479ac78a Peng Fan          2024-08-29  768  	/*
59090e479ac78a Peng Fan          2024-08-29  769  	 * KASAN can save its free meta data inside of the object at offset 0.
59090e479ac78a Peng Fan          2024-08-29  770  	 * If this meta data size is larger than 'orig_size', it will overlap
59090e479ac78a Peng Fan          2024-08-29  771  	 * the data redzone in [orig_size+1, object_size]. Thus, we adjust
59090e479ac78a Peng Fan          2024-08-29  772  	 * 'orig_size' to be as at least as big as KASAN's meta data.
59090e479ac78a Peng Fan          2024-08-29  773  	 */
59090e479ac78a Peng Fan          2024-08-29  774  	kasan_meta_size = kasan_metadata_size(s, true);
59090e479ac78a Peng Fan          2024-08-29 @775  	if (kasan_meta_size > orig_size)
59090e479ac78a Peng Fan          2024-08-29  776  		orig_size = kasan_meta_size;
59090e479ac78a Peng Fan          2024-08-29  777  
59090e479ac78a Peng Fan          2024-08-29  778  	p += get_info_end(s);
59090e479ac78a Peng Fan          2024-08-29  779  	p += sizeof(struct track) * 2;
59090e479ac78a Peng Fan          2024-08-29  780  
b6e5cef4d6df31 Harry Yoo         2026-01-13  781  	*(unsigned long *)p = orig_size;
59090e479ac78a Peng Fan          2024-08-29  782  }
59090e479ac78a Peng Fan          2024-08-29  783  

:::::: The code at line 775 was first introduced by commit
:::::: 59090e479ac78ae18facd4c58eb332562a23020e mm, slub: avoid zeroing kmalloc redzone

:::::: TO: Peng Fan <[email protected]>
:::::: CC: Vlastimil Babka <[email protected]>

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