Re: [v2 05/11] lib/test_hmm: test cases and support for zone device private THP

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

Hi Balbir,

kernel test robot noticed the following build warnings:

[auto build test WARNING on akpm-mm/mm-everything]
[also build test WARNING on next-20250731]
[cannot apply to akpm-mm/mm-nonmm-unstable shuah-kselftest/next shuah-kselftest/fixes linus/master v6.16]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Balbir-Singh/mm-zone_device-support-large-zone-device-private-folios/20250730-172600
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20250730092139.3890844-6-balbirs%40nvidia.com
patch subject: [v2 05/11] lib/test_hmm: test cases and support for zone device private THP
config: loongarch-allyesconfig (https://download.01.org/0day-ci/archive/20250731/202507311818.V6HUiudq-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 8f09b03aebb71c154f3bbe725c29e3f47d37c26e)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250731/202507311818.V6HUiudq-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/202507311818.V6HUiudq-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> lib/test_hmm.c:1111:6: warning: variable 'dst_pfns' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
    1111 |         if (!src_pfns)
         |             ^~~~~~~~~
   lib/test_hmm.c:1176:8: note: uninitialized use occurs here
    1176 |         kfree(dst_pfns);
         |               ^~~~~~~~
   lib/test_hmm.c:1111:2: note: remove the 'if' if its condition is always false
    1111 |         if (!src_pfns)
         |         ^~~~~~~~~~~~~~
    1112 |                 goto free_mem;
         |                 ~~~~~~~~~~~~~
   lib/test_hmm.c:1097:25: note: initialize the variable 'dst_pfns' to silence this warning
    1097 |         unsigned long *dst_pfns;
         |                                ^
         |                                 = NULL
   1 warning generated.


vim +1111 lib/test_hmm.c

  1084	
  1085	static int dmirror_migrate_to_device(struct dmirror *dmirror,
  1086					struct hmm_dmirror_cmd *cmd)
  1087	{
  1088		unsigned long start, end, addr;
  1089		unsigned long size = cmd->npages << PAGE_SHIFT;
  1090		struct mm_struct *mm = dmirror->notifier.mm;
  1091		struct vm_area_struct *vma;
  1092		struct dmirror_bounce bounce;
  1093		struct migrate_vma args = { 0 };
  1094		unsigned long next;
  1095		int ret;
  1096		unsigned long *src_pfns;
  1097		unsigned long *dst_pfns;
  1098	
  1099		start = cmd->addr;
  1100		end = start + size;
  1101		if (end < start)
  1102			return -EINVAL;
  1103	
  1104		/* Since the mm is for the mirrored process, get a reference first. */
  1105		if (!mmget_not_zero(mm))
  1106			return -EINVAL;
  1107	
  1108		ret = -ENOMEM;
  1109		src_pfns = kvcalloc(PTRS_PER_PTE, sizeof(*src_pfns),
  1110				  GFP_KERNEL | __GFP_NOFAIL);
> 1111		if (!src_pfns)
  1112			goto free_mem;
  1113	
  1114		dst_pfns = kvcalloc(PTRS_PER_PTE, sizeof(*dst_pfns),
  1115				  GFP_KERNEL | __GFP_NOFAIL);
  1116		if (!dst_pfns)
  1117			goto free_mem;
  1118	
  1119		ret = 0;
  1120		mmap_read_lock(mm);
  1121		for (addr = start; addr < end; addr = next) {
  1122			vma = vma_lookup(mm, addr);
  1123			if (!vma || !(vma->vm_flags & VM_READ)) {
  1124				ret = -EINVAL;
  1125				goto out;
  1126			}
  1127			next = min(end, addr + (PTRS_PER_PTE << PAGE_SHIFT));
  1128			if (next > vma->vm_end)
  1129				next = vma->vm_end;
  1130	
  1131			args.vma = vma;
  1132			args.src = src_pfns;
  1133			args.dst = dst_pfns;
  1134			args.start = addr;
  1135			args.end = next;
  1136			args.pgmap_owner = dmirror->mdevice;
  1137			args.flags = MIGRATE_VMA_SELECT_SYSTEM |
  1138					MIGRATE_VMA_SELECT_COMPOUND;
  1139			ret = migrate_vma_setup(&args);
  1140			if (ret)
  1141				goto out;
  1142	
  1143			pr_debug("Migrating from sys mem to device mem\n");
  1144			dmirror_migrate_alloc_and_copy(&args, dmirror);
  1145			migrate_vma_pages(&args);
  1146			dmirror_migrate_finalize_and_map(&args, dmirror);
  1147			migrate_vma_finalize(&args);
  1148		}
  1149		mmap_read_unlock(mm);
  1150		mmput(mm);
  1151	
  1152		/*
  1153		 * Return the migrated data for verification.
  1154		 * Only for pages in device zone
  1155		 */
  1156		ret = dmirror_bounce_init(&bounce, start, size);
  1157		if (ret)
  1158			goto free_mem;
  1159		mutex_lock(&dmirror->mutex);
  1160		ret = dmirror_do_read(dmirror, start, end, &bounce);
  1161		mutex_unlock(&dmirror->mutex);
  1162		if (ret == 0) {
  1163			if (copy_to_user(u64_to_user_ptr(cmd->ptr), bounce.ptr,
  1164					 bounce.size))
  1165				ret = -EFAULT;
  1166		}
  1167		cmd->cpages = bounce.cpages;
  1168		dmirror_bounce_fini(&bounce);
  1169		goto free_mem;
  1170	
  1171	out:
  1172		mmap_read_unlock(mm);
  1173		mmput(mm);
  1174	free_mem:
  1175		kfree(src_pfns);
  1176		kfree(dst_pfns);
  1177		return ret;
  1178	}
  1179	

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