On Thu, Jun 1, 2023 at 11:36 AM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote:
>
> On Thu, Jun 1, 2023 at 11:34 AM Nathan Chancellor <nathan@xxxxxxxxxx> wrote:
> >
> > 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.
> >
> > This condition used to return -ENOMEM by going to the shrink label, so
> > set ret to -ENOMEM in the if block explicitly to avoid using it
> > uninitialized.
> >
> > Fixes: 6804144bf1cf ("zswap: do not shrink if cgroup may not zswap")
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Closes: https://lore.kernel.org/202306011435.2BxsHFUE-lkp@xxxxxxxxx/
> > Closes: https://lore.kernel.org/202306012152.o4FL7Y6J-lkp@xxxxxxxxx/
> > Closes: https://github.com/ClangBuiltLinux/linux/issues/1861
> > Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
>
> Thanks!
>
> Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
>
> > ---
> > Changes in v2:
> > - Change ret to -ENOMEM to match this condition's previous return value
> > (Yosry)
> > - Link to v1: https://lore.kernel.org/r/20230601-zswap-cgroup-wsometimes-uninitialized-v1-1-35debdd19293@xxxxxxxxxx
> > ---
> > mm/zswap.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index cff93643a6ab..30092d9a3b23 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 = -ENOMEM;
> > 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@xxxxxxxxxx>
> >
Acked-by: Nhat Pham <nphamcs@xxxxxxxxx>
