[PATCH] zswap: Avoid uninitialized use of ret in zswap_frontswap_store()

[Nathan Chancellor <nathan@kernel.org>]

Clang warns:

  mm/zswap.c:1183:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
   1183 |         if (objcg && !obj_cgroup_may_zswap(objcg))
        |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  mm/zswap.c:1327:9: note: uninitialized use occurs here
   1327 |         return ret;
        |                ^~~
  mm/zswap.c:1183:2: note: remove the 'if' if its condition is always false
   1183 |         if (objcg && !obj_cgroup_may_zswap(objcg))
        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   1184 |                 goto reject;
        | ~~~~~~~~~~~~~~~~~~~~~~~~~~~
  mm/zswap.c:1158:9: note: initialize the variable 'ret' to silence this warning
   1158 |         int ret;
        |                ^
        |                 = 0
  1 error generated.

Set ret to -EINVAL, which seems to best match the situation the comment
mentions and matches an earlier bailout due to an unsupported type or
situation.

Fixes: 6804144bf1cf ("zswap: do not shrink if cgroup may not zswap")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/202306011435.2BxsHFUE-lkp@intel.com/
Closes: https://lore.kernel.org/202306012152.o4FL7Y6J-lkp@intel.com/
Closes: https://github.com/ClangBuiltLinux/linux/issues/1861
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 mm/zswap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index cff93643a6ab..e8313e2f5807 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1180,8 +1180,10 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 	 * local cgroup limits.
 	 */
 	objcg = get_obj_cgroup_from_page(page);
-	if (objcg && !obj_cgroup_may_zswap(objcg))
+	if (objcg && !obj_cgroup_may_zswap(objcg)) {
+		ret = -EINVAL;
 		goto reject;
+	}
 
 	/* reclaim space if needed */
 	if (zswap_is_full()) {

---
base-commit: b2424568bd9b947b2698b693ff24fec63bb4b36a
change-id: 20230601-zswap-cgroup-wsometimes-uninitialized-b549ff4247ed

Best regards,
-- 
Nathan Chancellor <nathan@kernel.org>