Re: [PATCH v3 3/7] iommu/arm-smmu-v3: Introduce a per-domain arm_smmu_invs array

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

Hi Nicolin,

kernel test robot noticed the following build warnings:

[auto build test WARNING on soc/for-next]
[also build test WARNING on linus/master v6.18-rc1 next-20251016]
[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/Nicolin-Chen/iommu-arm-smmu-v3-Explicitly-set-smmu_domain-stage-for-SVA/20251016-034754
base:   https://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git for-next
patch link:    https://lore.kernel.org/r/345bb7703ebd19992694758b47e371900267fa0e.1760555863.git.nicolinc%40nvidia.com
patch subject: [PATCH v3 3/7] iommu/arm-smmu-v3: Introduce a per-domain arm_smmu_invs array
config: arm64-randconfig-001-20251017 (https://download.01.org/0day-ci/archive/20251017/202510170345.lO7fR7ao-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/20251017/202510170345.lO7fR7ao-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/202510170345.lO7fR7ao-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c:1170:7: warning: variable 'cmp' is uninitialized when used here [-Wuninitialized]
    1170 |                 if (cmp <= 0 && !refcount_read(&invs->inv[i].users)) {
         |                     ^~~
   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c:1167:10: note: initialize the variable 'cmp' to silence this warning
    1167 |                 int cmp;
         |                        ^
         |                         = 0
   1 warning generated.


vim +/cmp +1170 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

  1132	
  1133	/**
  1134	 * arm_smmu_invs_unref() - Find in @invs for all entries in @to_unref, decrease
  1135	 *                         the user counts without deletions
  1136	 * @invs: the base invalidation array
  1137	 * @to_unref: an array of invlidations to decrease their user counts
  1138	 * @flush_fn: A callback function to invoke, when an entry's user count reduces
  1139	 *            to 0
  1140	 *
  1141	 * Return: the number of trash entries in the array, for arm_smmu_invs_purge()
  1142	 *
  1143	 * This function will not fail. Any entry with users=0 will be marked as trash.
  1144	 * All tailing trash entries in the array will be dropped. And the size of the
  1145	 * array will be trimmed properly. All trash entries in-between will remain in
  1146	 * the @invs until being completely deleted by the next arm_smmu_invs_merge()
  1147	 * or an arm_smmu_invs_purge() function call.
  1148	 *
  1149	 * This function must be locked and serialized with arm_smmu_invs_merge() and
  1150	 * arm_smmu_invs_purge(), but do not lockdep on any mutex for KUNIT test.
  1151	 *
  1152	 * Note that the final @invs->num_invs might not reflect the actual number of
  1153	 * invalidations due to trash entries. Any reader should take the read lock to
  1154	 * iterate each entry and check its users counter till the last entry.
  1155	 */
  1156	VISIBLE_IF_KUNIT
  1157	size_t arm_smmu_invs_unref(struct arm_smmu_invs *invs,
  1158				   struct arm_smmu_invs *to_unref,
  1159				   void (*flush_fn)(struct arm_smmu_inv *inv))
  1160	{
  1161		unsigned long flags;
  1162		size_t num_trashes = 0;
  1163		size_t num_invs = 0;
  1164		size_t i, j;
  1165	
  1166		for (i = j = 0; i != invs->num_invs || j != to_unref->num_invs;) {
  1167			int cmp;
  1168	
  1169			/* Skip any existing trash entry */
> 1170			if (cmp <= 0 && !refcount_read(&invs->inv[i].users)) {
  1171				num_trashes++;
  1172				i++;
  1173				continue;
  1174			}
  1175	
  1176			cmp = arm_smmu_invs_cmp(invs, i, to_unref, j);
  1177			if (cmp < 0) {
  1178				/* not found in to_unref, leave alone */
  1179				i++;
  1180				num_invs = i;
  1181			} else if (cmp == 0) {
  1182				/* same item */
  1183				if (refcount_dec_and_test(&invs->inv[i].users)) {
  1184					/* KUNIT test doesn't pass in a flush_fn */
  1185					if (flush_fn)
  1186						flush_fn(&invs->inv[i]);
  1187					num_trashes++;
  1188				} else {
  1189					num_invs = i + 1;
  1190				}
  1191				i++;
  1192				j++;
  1193			} else {
  1194				/* item in to_unref is not in invs or already a trash */
  1195				WARN_ON(true);
  1196				j++;
  1197			}
  1198		}
  1199	
  1200		/* Exclude any tailing trash */
  1201		num_trashes -= invs->num_invs - num_invs;
  1202	
  1203		/* The lock is required to fence concurrent ATS operations. */
  1204		write_lock_irqsave(&invs->rwlock, flags);
  1205		WRITE_ONCE(invs->num_invs, num_invs); /* Remove tailing trash entries */
  1206		write_unlock_irqrestore(&invs->rwlock, flags);
  1207	
  1208		return num_trashes;
  1209	}
  1210	EXPORT_SYMBOL_IF_KUNIT(arm_smmu_invs_unref);
  1211	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki