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

[Kairui Song <ryncsn@gmail.com>]

On Wed, Feb 18, 2026 at 06:40:16PM +0800, kernel test robot wrote:
> 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.

Nice catch from the bot. It's a new added sanity check in V3 just
in case the swap count maybe grow larger than UINT_MAX, which should
never happen, but just in case.

I really should just use the existing helper macro for that:

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 801d8092be51..34b38255f72a 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1624,7 +1624,7 @@ static int __swap_cluster_dup_entry(struct swap_cluster_info *ci,
                }
        } else if (count == SWP_TB_COUNT_MAX) {
                VM_WARN_ON_ONCE(ci->extend_table[ci_off] >=
-                               (BIT(BITS_PER_TYPE(ci->extend_table[0]))) - 1);
+                               type_max(typeof(ci->extend_table[0])));
                ++ci->extend_table[ci_off];
        } else {
                /* Never happens unless counting went wrong */