On Fri, Jan 12, 2024 at 12:42:37AM -0700, Yu Zhao wrote:
> On Fri, Jan 12, 2024 at 12:13 AM Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> >
> > Hello Yu Zhao,
> >
> > The patch 081488051d28: "mm/mglru: fix underprotected page cache"
> > from Dec 7, 2023 (linux-next), leads to the following Smatch static
> > checker warning:
> >
> > mm/workingset.c:318 lru_gen_refault()
> > warn: always true condition '(refs >= ((((1))) << (__builtin_choose_expr((4 == 4), (((2) < (64 - 26 - 3 - 3 - 0 - 10 - 0 - (8 + 14))) ?(2):(64 - 26 - 3 - 3 - 0 - 10 - 0 - (8 + 14))), ))) - 1) => (s32min-s32max >= 0)'
> >
> > mm/workingset.c
> > 308 atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]);
> > 309 mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta);
> > 310
> > 311 /*
> > 312 * Count the following two cases as stalls:
> > 313 * 1. For pages accessed through page tables, hotter pages pushed out
> > 314 * hot pages which refaulted immediately.
> > 315 * 2. For pages accessed multiple times through file descriptors,
> > 316 * they would have been protected by sort_folio().
> > 317 */
> > --> 318 if (lru_gen_in_fault() || refs >= BIT(LRU_REFS_WIDTH) - 1) {
> > ^^^^^^^^^^^^^^^^^^^^^^^
> > In my x86 allmodconfig this is zero and refs is always >= 0. This could
> > be intentional, but I thought it was worth checking.
>
> Appreciate the manual work!
>
> This indeed is intentional if LRU_REFS_WIDTH is 0. What would be the
> best way to suppress this warning?
No need.
These warnings are a one time thing. Ignore the false positives. If
people are curious in the future they can find this conversation on
lore.
regards,
dan carpenter
