Re: [PATCH v3 09/12] mm, swap: use the swap table to track the swap count

[kernel test robot <lkp@intel.com>]

Hi Kairui,

kernel test robot noticed the following build warnings:

[auto build test WARNING on d9982f38eb6e9a0cb6bdd1116cc87f75a1084aad]

url:    https://github.com/intel-lab-lkp/linux/commits/Kairui-Song-via-B4-Relay/mm-swap-protect-si-swap_file-properly-and-use-as-a-mount-indicator/20260218-040852
base:   d9982f38eb6e9a0cb6bdd1116cc87f75a1084aad
patch link:    https://lore.kernel.org/r/20260218-swap-table-p3-v3-9-f4e34be021a7%40tencent.com
patch subject: [PATCH v3 09/12] mm, swap: use the swap table to track the swap count
config: i386-buildonly-randconfig-001-20260218 (https://download.01.org/0day-ci/archive/20260218/202602181835.58TEynxc-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/20260218/202602181835.58TEynxc-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/202602181835.58TEynxc-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> mm/swapfile.c:1627:6: warning: shift count >= width of type [-Wshift-count-overflow]
    1626 |                 VM_WARN_ON_ONCE(ci->extend_table[ci_off] >=
         |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    1627 |                                 (BIT(BITS_PER_TYPE(ci->extend_table[0]))) - 1);
         |                                 ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/vdso/bits.h:7:26: note: expanded from macro 'BIT'
       7 | #define BIT(nr)                 (UL(1) << (nr))
         |                                        ^
   include/linux/mmdebug.h:123:50: note: expanded from macro 'VM_WARN_ON_ONCE'
     123 | #define VM_WARN_ON_ONCE(cond) (void)WARN_ON_ONCE(cond)
         |                                     ~~~~~~~~~~~~~^~~~~
   include/asm-generic/bug.h:120:25: note: expanded from macro 'WARN_ON_ONCE'
     120 |         int __ret_warn_on = !!(condition);                              \
         |                                ^~~~~~~~~
   1 warning generated.


vim +1627 mm/swapfile.c

  1596	
  1597	/* Increase the swap count of one slot. */
  1598	static int __swap_cluster_dup_entry(struct swap_cluster_info *ci,
  1599					    unsigned int ci_off)
  1600	{
  1601		int count;
  1602		unsigned long swp_tb;
  1603	
  1604		lockdep_assert_held(&ci->lock);
  1605		swp_tb = __swap_table_get(ci, ci_off);
  1606		/* Bad or special slots can't be handled */
  1607		if (WARN_ON_ONCE(swp_tb_is_bad(swp_tb)))
  1608			return -EINVAL;
  1609		count = __swp_tb_get_count(swp_tb);
  1610		/* Must be either cached or have a count already */
  1611		if (WARN_ON_ONCE(!count && !swp_tb_is_folio(swp_tb)))
  1612			return -ENOENT;
  1613	
  1614		if (likely(count < (SWP_TB_COUNT_MAX - 1))) {
  1615			__swap_table_set(ci, ci_off, __swp_tb_mk_count(swp_tb, count + 1));
  1616			VM_WARN_ON_ONCE(ci->extend_table && ci->extend_table[ci_off]);
  1617		} else if (count == (SWP_TB_COUNT_MAX - 1)) {
  1618			if (ci->extend_table) {
  1619				VM_WARN_ON_ONCE(ci->extend_table[ci_off]);
  1620				ci->extend_table[ci_off] = SWP_TB_COUNT_MAX;
  1621				__swap_table_set(ci, ci_off, __swp_tb_mk_count(swp_tb, SWP_TB_COUNT_MAX));
  1622			} else {
  1623				return -ENOMEM;
  1624			}
  1625		} else if (count == SWP_TB_COUNT_MAX) {
  1626			VM_WARN_ON_ONCE(ci->extend_table[ci_off] >=
> 1627					(BIT(BITS_PER_TYPE(ci->extend_table[0]))) - 1);
  1628			++ci->extend_table[ci_off];
  1629		} else {
  1630			/* Never happens unless counting went wrong */
  1631			WARN_ON_ONCE(1);
  1632		}
  1633	
  1634		return 0;
  1635	}
  1636	

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