Hi Dongsheng,
On Fri, Aug 22, 2025 at 02:53:42PM +0800, Dongsheng Yang wrote:
>
> 在 8/22/2025 4:09 AM, Nathan Chancellor 写道:
> > When building for a 32-bit platform (such as ARCH=i386 allmodconfig),
> > there is a modpost error:
> >
> > ERROR: modpost: "__umoddi3" [drivers/md/dm-pcache/dm-pcache.ko]
> > undefined!
> >
> > Hacking up the driver Makefile to allow building into the kernel shows
> > that the division comes from get_kset_id(), which is inlined into
> > cache_key_append() in cache_key.c.
> >
> > Use the helper div_u64_rem() to avoid emitting a libcall on 32-bit targets.
> >
> > Fixes: fd5cc4922bef ("dm-pcache: add persistent cache target in
> > device-mapper")
> > Signed-off-by: Nathan Chancellor <[email protected]>
> > ---
> > drivers/md/dm-pcache/cache.h | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/md/dm-pcache/cache.h b/drivers/md/dm-pcache/cache.h
> > index b3b361cc406e..b10e721ab1b7 100644
> > --- a/drivers/md/dm-pcache/cache.h
> > +++ b/drivers/md/dm-pcache/cache.h
> > @@ -373,7 +373,9 @@ static inline void *get_key_head_addr(struct
> > pcache_cache *cache)
> > static inline u32 get_kset_id(struct pcache_cache *cache, u64 off)
> > {
> > - return (off >> PCACHE_CACHE_SUBTREE_SIZE_SHIFT) % cache->n_ksets;
> > + u32 rem;
> > + div_u64_rem(off >> PCACHE_CACHE_SUBTREE_SIZE_SHIFT, cache->n_ksets,
> > &rem);
> > + return rem;
> > }
>
>
> Hi Nathan,
>
> Thanx for your fix. It looks good to me.
>
> Just one nit about the variable name. I prefer kset_id to rem.
Thanks, seems entirely reasonable, thanks for sending the diff!
> Mikulas, if this looks good to you, could you apply this change to dm-6.18?
>
> diff --git a/drivers/md/dm-pcache/cache.h b/drivers/md/dm-pcache/cache.h
> index b3b361cc406e..f005c9d9a7aa 100644
> --- a/drivers/md/dm-pcache/cache.h
> +++ b/drivers/md/dm-pcache/cache.h
> @@ -373,7 +373,11 @@ static inline void *get_key_head_addr(struct
> pcache_cache *cache)
>
> static inline u32 get_kset_id(struct pcache_cache *cache, u64 off)
> {
> - return (off >> PCACHE_CACHE_SUBTREE_SIZE_SHIFT) % cache->n_ksets;
> + u32 kset_id;
> +
> + div_u64_rem(off >> PCACHE_CACHE_SUBTREE_SIZE_SHIFT, cache->n_ksets,
> &kset_id);
> +
> + return kset_id;
> }
>
> static inline struct pcache_cache_kset *get_kset(struct pcache_cache
> *cache, u32 kset_id)
>
> > re
> > static inline struct pcache_cache_kset *get_kset(struct pcache_cache
> > *cache, u32 kset_id)
> >
> > ---
> > base-commit: fd5cc4922bef4b3c3cd0452f38dcfd066322e9a9
> > change-id: 20250821-dm-pcache-fix-32-bit-div-err-4f0695e94784
> >
> > Best regards,
> > --
> > Nathan Chancellor <[email protected]>
> >
