Re: [PATCH v2 2/3] mm/swap: use swap_ops to register swap device's methods

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

Hi Barry,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Barry-Song/mm-swap-rename-mm-page_io-c-to-mm-swap_io-c/20260328-170852
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20260328075812.11060-3-21cnbao%40gmail.com
patch subject: [PATCH v2 2/3] mm/swap: use swap_ops to register swap device's methods
config: um-randconfig-r072-20260329 (https://download.01.org/0day-ci/archive/20260329/202603291919.Y8MwFsok-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
smatch: v0.5.0-9004-gb810ac53
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260329/202603291919.Y8MwFsok-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/202603291919.Y8MwFsok-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from include/asm-generic/bug.h:7,
                    from ./arch/um/include/generated/asm/bug.h:1,
                    from arch/x86/include/asm/alternative.h:9,
                    from arch/x86/um/asm/barrier.h:6,
                    from include/linux/list.h:11,
                    from include/linux/module.h:12,
                    from mm/zswap.c:16:
   mm/zswap.c: In function 'zswap_writeback_entry':
>> mm/zswap.c:1057:26: error: 'sis' undeclared (first use in this function); did you mean 'si'?
    1057 |         VM_WARN_ON_ONCE(!sis->ops || !sis->ops->write_folio);
         |                          ^~~
   include/linux/once_lite.h:28:41: note: in definition of macro 'DO_ONCE_LITE_IF'
      28 |                 bool __ret_do_once = !!(condition);                     \
         |                                         ^~~~~~~~~
   include/linux/mmdebug.h:123:37: note: in expansion of macro 'WARN_ON_ONCE'
     123 | #define VM_WARN_ON_ONCE(cond) (void)WARN_ON_ONCE(cond)
         |                                     ^~~~~~~~~~~~
   mm/zswap.c:1057:9: note: in expansion of macro 'VM_WARN_ON_ONCE'
    1057 |         VM_WARN_ON_ONCE(!sis->ops || !sis->ops->write_folio);
         |         ^~~~~~~~~~~~~~~
   mm/zswap.c:1057:26: note: each undeclared identifier is reported only once for each function it appears in
    1057 |         VM_WARN_ON_ONCE(!sis->ops || !sis->ops->write_folio);
         |                          ^~~
   include/linux/once_lite.h:28:41: note: in definition of macro 'DO_ONCE_LITE_IF'
      28 |                 bool __ret_do_once = !!(condition);                     \
         |                                         ^~~~~~~~~
   include/linux/mmdebug.h:123:37: note: in expansion of macro 'WARN_ON_ONCE'
     123 | #define VM_WARN_ON_ONCE(cond) (void)WARN_ON_ONCE(cond)
         |                                     ^~~~~~~~~~~~
   mm/zswap.c:1057:9: note: in expansion of macro 'VM_WARN_ON_ONCE'
    1057 |         VM_WARN_ON_ONCE(!sis->ops || !sis->ops->write_folio);
         |         ^~~~~~~~~~~~~~~


vim +1057 mm/zswap.c

   971	
   972	/*********************************
   973	* writeback code
   974	**********************************/
   975	/*
   976	 * Attempts to free an entry by adding a folio to the swap cache,
   977	 * decompressing the entry data into the folio, and issuing a
   978	 * bio write to write the folio back to the swap device.
   979	 *
   980	 * This can be thought of as a "resumed writeback" of the folio
   981	 * to the swap device.  We are basically resuming the same swap
   982	 * writeback path that was intercepted with the zswap_store()
   983	 * in the first place.  After the folio has been decompressed into
   984	 * the swap cache, the compressed version stored by zswap can be
   985	 * freed.
   986	 */
   987	static int zswap_writeback_entry(struct zswap_entry *entry,
   988					 swp_entry_t swpentry)
   989	{
   990		struct xarray *tree;
   991		pgoff_t offset = swp_offset(swpentry);
   992		struct folio *folio;
   993		struct mempolicy *mpol;
   994		bool folio_was_allocated;
   995		struct swap_info_struct *si;
   996		int ret = 0;
   997	
   998		/* try to allocate swap cache folio */
   999		si = get_swap_device(swpentry);
  1000		if (!si)
  1001			return -EEXIST;
  1002	
  1003		mpol = get_task_policy(current);
  1004		folio = swap_cache_alloc_folio(swpentry, GFP_KERNEL, mpol,
  1005					       NO_INTERLEAVE_INDEX, &folio_was_allocated);
  1006		put_swap_device(si);
  1007		if (!folio)
  1008			return -ENOMEM;
  1009	
  1010		/*
  1011		 * Found an existing folio, we raced with swapin or concurrent
  1012		 * shrinker. We generally writeback cold folios from zswap, and
  1013		 * swapin means the folio just became hot, so skip this folio.
  1014		 * For unlikely concurrent shrinker case, it will be unlinked
  1015		 * and freed when invalidated by the concurrent shrinker anyway.
  1016		 */
  1017		if (!folio_was_allocated) {
  1018			ret = -EEXIST;
  1019			goto out;
  1020		}
  1021	
  1022		/*
  1023		 * folio is locked, and the swapcache is now secured against
  1024		 * concurrent swapping to and from the slot, and concurrent
  1025		 * swapoff so we can safely dereference the zswap tree here.
  1026		 * Verify that the swap entry hasn't been invalidated and recycled
  1027		 * behind our backs, to avoid overwriting a new swap folio with
  1028		 * old compressed data. Only when this is successful can the entry
  1029		 * be dereferenced.
  1030		 */
  1031		tree = swap_zswap_tree(swpentry);
  1032		if (entry != xa_load(tree, offset)) {
  1033			ret = -ENOMEM;
  1034			goto out;
  1035		}
  1036	
  1037		if (!zswap_decompress(entry, folio)) {
  1038			ret = -EIO;
  1039			goto out;
  1040		}
  1041	
  1042		xa_erase(tree, offset);
  1043	
  1044		count_vm_event(ZSWPWB);
  1045		if (entry->objcg)
  1046			count_objcg_events(entry->objcg, ZSWPWB, 1);
  1047	
  1048		zswap_entry_free(entry);
  1049	
  1050		/* folio is up to date */
  1051		folio_mark_uptodate(folio);
  1052	
  1053		/* move it to the tail of the inactive list after end_writeback */
  1054		folio_set_reclaim(folio);
  1055	
  1056		/* start writeback */
> 1057		VM_WARN_ON_ONCE(!sis->ops || !sis->ops->write_folio);
  1058		si->ops->write_folio(si, folio, NULL);
  1059	
  1060	out:
  1061		if (ret && ret != -EEXIST) {
  1062			swap_cache_del_folio(folio);
  1063			folio_unlock(folio);
  1064		}
  1065		folio_put(folio);
  1066		return ret;
  1067	}
  1068	

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