Re: [PATCH] powerpc: fix "sz" set but not used

From: Michael Ellerman
Date: Thu Feb 28 2019 - 22:24:25 EST


Qian Cai <cai@xxxxxx> writes:
> arch/powerpc/mm/hugetlbpage-hash64.c: In function '__hash_page_huge':
> arch/powerpc/mm/hugetlbpage-hash64.c:29:28: warning: variable 'sz' set
> but not used [-Wunused-but-set-variable]

It's always nice to know *why* it's not used.

It's unlikely, but not impossible, that it's a bug that the variable is
not used.

To find out why:

$ git log --oneline -S sz arch/powerpc/mm/hugetlbpage-hash64.c
0895ecda7942 powerpc/mm: Bring hugepage PTE accessor functions back into sync with normal accessors
883a3e523672 powerpc/mm: Split hash MMU specific hugepage code into a new file

Then we look at those, and see the the first one did:

@@ -89,8 +62,7 @@ int __hash_page_huge(unsigned long ea, unsigned long access, unsigned long vsid,
if (!cpu_has_feature(CPU_FTR_COHERENT_ICACHE))
/* No CPU has hugepages but lacks no execute, so we
* don't need to worry about that case */
- rflags = hash_huge_page_do_lazy_icache(rflags, __pte(old_pte),
- trap, sz);
+ rflags = hash_page_do_lazy_icache(rflags, __pte(old_pte), trap);


And if you read the commit log it's pretty clear the change was
deliberate and so sz should indeed be removed.

I've applied this as-is, no need to send a v2.

cheers

> diff --git a/arch/powerpc/mm/hugetlbpage-hash64.c b/arch/powerpc/mm/hugetlbpage-hash64.c
> index 2e6a8f9345d3..f6b09edc5e6e 100644
> --- a/arch/powerpc/mm/hugetlbpage-hash64.c
> +++ b/arch/powerpc/mm/hugetlbpage-hash64.c
> @@ -26,7 +26,7 @@ int __hash_page_huge(unsigned long ea, unsigned long access, unsigned long vsid,
> real_pte_t rpte;
> unsigned long vpn;
> unsigned long old_pte, new_pte;
> - unsigned long rflags, pa, sz;
> + unsigned long rflags, pa;
> long slot, offset;
>
> BUG_ON(shift != mmu_psize_defs[mmu_psize].shift);
> @@ -73,7 +73,6 @@ int __hash_page_huge(unsigned long ea, unsigned long access, unsigned long vsid,
> offset = PTRS_PER_PMD;
> rpte = __real_pte(__pte(old_pte), ptep, offset);
>
> - sz = ((1UL) << shift);
> if (!cpu_has_feature(CPU_FTR_COHERENT_ICACHE))
> /* No CPU has hugepages but lacks no execute, so we
> * don't need to worry about that case */
> --
> 2.17.2 (Apple Git-113)