The commit 58629c0dc349 ("powerpc/powernv/npu: Fault user page into the
hypervisor's pagetable") introduced a variable "c" to be used in
__get_user() and __get_user_nocheck() which need to stay as macros for
performance reasons, and "c" is not actually used in
pnv_npu2_handle_fault(),
arch/powerpc/platforms/powernv/npu-dma.c: In function 'pnv_npu2_handle_fault':
arch/powerpc/platforms/powernv/npu-dma.c:1122:7: warning: variable 'c'
set but not used [-Wunused-but-set-variable]
Fixed it by appending the __maybe_unused attribute, so compilers would
ignore it.
Signed-off-by: Qian Cai <[email protected]>
---
arch/powerpc/platforms/powernv/npu-dma.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/platforms/powernv/npu-dma.c b/arch/powerpc/platforms/powernv/npu-dma.c
index 495550432f3d..5bbe59573ee6 100644
--- a/arch/powerpc/platforms/powernv/npu-dma.c
+++ b/arch/powerpc/platforms/powernv/npu-dma.c
@@ -1119,7 +1119,8 @@ int pnv_npu2_handle_fault(struct npu_context *context, uintptr_t *ea,
int i, is_write;
struct page *page[1];
const char __user *u;
- char c;
+ /* To silence a -Wunused-but-set-variable warning. */
+ char c __maybe_unused;
/* mmap_sem should be held so the struct_mm must be present */
struct mm_struct *mm = context->mm;
--
2.20.1 (Apple Git-117)
Le 23/05/2019 à 04:31, Qian Cai a écrit :
> The commit 58629c0dc349 ("powerpc/powernv/npu: Fault user page into the
> hypervisor's pagetable") introduced a variable "c" to be used in
> __get_user() and __get_user_nocheck() which need to stay as macros for
> performance reasons, and "c" is not actually used in
> pnv_npu2_handle_fault(),
>
> arch/powerpc/platforms/powernv/npu-dma.c: In function 'pnv_npu2_handle_fault':
> arch/powerpc/platforms/powernv/npu-dma.c:1122:7: warning: variable 'c'
> set but not used [-Wunused-but-set-variable]
>
> Fixed it by appending the __maybe_unused attribute, so compilers would
> ignore it.
You are not fixing the problem, you are just hiding it.
If the result of __get_user() is unneeded, it means __get_user() is not
the good function to use.
Should use fault_in_pages_readable() instead.
A similar warning was fixed in commit 9f9eae5ce717 ("powerpc/kvm: Prefer
fault_in_pages_readable function")
See
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/powerpc?id=9f9eae5ce
>
> Signed-off-by: Qian Cai <[email protected]>
You should add a Fixes: tag
58629c0dc349 ("powerpc/powernv/npu: Fault user page into the
hypervisor's pagetable")
Christophe
> ---
> arch/powerpc/platforms/powernv/npu-dma.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/platforms/powernv/npu-dma.c b/arch/powerpc/platforms/powernv/npu-dma.c
> index 495550432f3d..5bbe59573ee6 100644
> --- a/arch/powerpc/platforms/powernv/npu-dma.c
> +++ b/arch/powerpc/platforms/powernv/npu-dma.c
> @@ -1119,7 +1119,8 @@ int pnv_npu2_handle_fault(struct npu_context *context, uintptr_t *ea,
> int i, is_write;
> struct page *page[1];
> const char __user *u;
> - char c;
> + /* To silence a -Wunused-but-set-variable warning. */
> + char c __maybe_unused;
>
> /* mmap_sem should be held so the struct_mm must be present */
> struct mm_struct *mm = context->mm;
>
On Thu, May 23, 2019 at 09:26:53AM +0200, Christophe Leroy wrote:
> You are not fixing the problem, you are just hiding it.
>
> If the result of __get_user() is unneeded, it means __get_user() is not the
> good function to use.
>
> Should use fault_in_pages_readable() instead.
Also it is not just the variable that is unused, but that whole
function. I'll resend my series to remote it in a bit.