[PATCHv3, resend] powerpc: mm: radix_tlb: rearrange the if-else block

[PATCHv3, resend] powerpc: mm: radix_tlb: rearrange the if-else block

[Anders Roxell]

Clang warns:

arch/powerpc/mm/book3s64/radix_tlb.c:1191:23: error: variable 'hstart' is uninitialized when used here [-Werror,-Wuninitialized]
                                __tlbiel_va_range(hstart, hend, pid,
                                                  ^~~~~~
arch/powerpc/mm/book3s64/radix_tlb.c:1175:23: note: initialize the variable 'hstart' to silence this warning
                unsigned long hstart, hend;
                                    ^
                                     = 0
arch/powerpc/mm/book3s64/radix_tlb.c:1191:31: error: variable 'hend' is uninitialized when used here [-Werror,-Wuninitialized]
                                __tlbiel_va_range(hstart, hend, pid,
                                                          ^~~~
arch/powerpc/mm/book3s64/radix_tlb.c:1175:29: note: initialize the variable 'hend' to silence this warning
                unsigned long hstart, hend;
                                          ^
                                           = 0
2 errors generated.

Rework the 'if (IS_ENABLE(CONFIG_TRANSPARENT_HUGEPAGE))' so hstart/hend
always gets initialized, this will silence the warnings. That will also
simplify the 'else' path. Clang is getting confused with these warnings,
but the warnings is a false-positive.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
---
 arch/powerpc/mm/book3s64/radix_tlb.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c
index 4e29b619578c..6d7a1ef723e6 100644
--- a/arch/powerpc/mm/book3s64/radix_tlb.c
+++ b/arch/powerpc/mm/book3s64/radix_tlb.c
@@ -1179,15 +1179,12 @@ static inline void __radix__flush_tlb_range(struct mm_struct *mm,
 			}
 		}
 	} else {
-		bool hflush = false;
+		bool hflush;
 		unsigned long hstart, hend;
 
-		if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
-			hstart = (start + PMD_SIZE - 1) & PMD_MASK;
-			hend = end & PMD_MASK;
-			if (hstart < hend)
-				hflush = true;
-		}
+		hstart = (start + PMD_SIZE - 1) & PMD_MASK;
+		hend = end & PMD_MASK;
+		hflush = IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && hstart < hend;
 
 		if (type == FLUSH_TYPE_LOCAL) {
 			asm volatile("ptesync": : :"memory");
-- 
2.35.1

Re: [PATCHv3, resend] powerpc: mm: radix_tlb: rearrange the if-else block

[Segher Boessenkool]

Hi!

On Wed, Aug 10, 2022 at 01:43:18PM +0200, Anders Roxell wrote:
> Clang warns:
> 
> arch/powerpc/mm/book3s64/radix_tlb.c:1191:23: error: variable 'hstart' is uninitialized when used here [-Werror,-Wuninitialized]
>                                 __tlbiel_va_range(hstart, hend, pid,
>                                                   ^~~~~~
> arch/powerpc/mm/book3s64/radix_tlb.c:1175:23: note: initialize the variable 'hstart' to silence this warning

This note often is bad advice: hiding problems instead of investigating
and solving them.  Bah.

If silencing warnings is your goal, look no further than "-w" :-)

> Rework the 'if (IS_ENABLE(CONFIG_TRANSPARENT_HUGEPAGE))' so hstart/hend
> always gets initialized, this will silence the warnings. That will also
> simplify the 'else' path. Clang is getting confused with these warnings,
> but the warnings is a false-positive.

If it is, please report that bug to clang?  It says "*is* uninitialized
when used here", there can not be false positives to statements like
that.  If the analysis was heutistical it should say "may be" or such.


Segher

Re: [PATCHv3, resend] powerpc: mm: radix_tlb: rearrange the if-else block

[Michael Ellerman]

Anders Roxell <anders.roxell@linaro.org> writes:
> Clang warns:
>
> arch/powerpc/mm/book3s64/radix_tlb.c:1191:23: error: variable 'hstart' is uninitialized when used here [-Werror,-Wuninitialized]
>                                 __tlbiel_va_range(hstart, hend, pid,
>                                                   ^~~~~~
> arch/powerpc/mm/book3s64/radix_tlb.c:1175:23: note: initialize the variable 'hstart' to silence this warning
>                 unsigned long hstart, hend;
>                                     ^
>                                      = 0
> arch/powerpc/mm/book3s64/radix_tlb.c:1191:31: error: variable 'hend' is uninitialized when used here [-Werror,-Wuninitialized]
>                                 __tlbiel_va_range(hstart, hend, pid,
>                                                           ^~~~
> arch/powerpc/mm/book3s64/radix_tlb.c:1175:29: note: initialize the variable 'hend' to silence this warning
>                 unsigned long hstart, hend;
>                                           ^
>                                            = 0
> 2 errors generated.

Which version & config are you building?

I don't see this warning in my test builds.

cheers

Re: [PATCHv3, resend] powerpc: mm: radix_tlb: rearrange the if-else block

[Anders Roxell]

On Thu, 11 Aug 2022 at 11:41, Michael Ellerman <mpe@ellerman.id.au> wrote:
>
> Anders Roxell <anders.roxell@linaro.org> writes:
> > Clang warns:
> >
> > arch/powerpc/mm/book3s64/radix_tlb.c:1191:23: error: variable 'hstart' is uninitialized when used here [-Werror,-Wuninitialized]
> >                                 __tlbiel_va_range(hstart, hend, pid,
> >                                                   ^~~~~~
> > arch/powerpc/mm/book3s64/radix_tlb.c:1175:23: note: initialize the variable 'hstart' to silence this warning
> >                 unsigned long hstart, hend;
> >                                     ^
> >                                      = 0
> > arch/powerpc/mm/book3s64/radix_tlb.c:1191:31: error: variable 'hend' is uninitialized when used here [-Werror,-Wuninitialized]
> >                                 __tlbiel_va_range(hstart, hend, pid,
> >                                                           ^~~~
> > arch/powerpc/mm/book3s64/radix_tlb.c:1175:29: note: initialize the variable 'hend' to silence this warning
> >                 unsigned long hstart, hend;
> >                                           ^
> >                                            = 0
> > 2 errors generated.
>
> Which version & config are you building?

clang-13, clang-14 and clang-nightly, configs are cell_defconfig and
maple_defconfig

I'm building with tuxmake [1] like this:
$ tuxmake --runtime podman --target-arch powerpc --toolchain clang-14
--kconfig cell_defconfig

Cheers,
Anders
[1] https://tuxmake.org/

Re: [PATCHv3, resend] powerpc: mm: radix_tlb: rearrange the if-else block

[Michael Ellerman]

On Wed, 10 Aug 2022 13:43:18 +0200, Anders Roxell wrote:
> Clang warns:
> 
> arch/powerpc/mm/book3s64/radix_tlb.c:1191:23: error: variable 'hstart' is uninitialized when used here [-Werror,-Wuninitialized]
>                                 __tlbiel_va_range(hstart, hend, pid,
>                                                   ^~~~~~
> arch/powerpc/mm/book3s64/radix_tlb.c:1175:23: note: initialize the variable 'hstart' to silence this warning
>                 unsigned long hstart, hend;
>                                     ^
>                                      = 0
> arch/powerpc/mm/book3s64/radix_tlb.c:1191:31: error: variable 'hend' is uninitialized when used here [-Werror,-Wuninitialized]
>                                 __tlbiel_va_range(hstart, hend, pid,
>                                                           ^~~~
> arch/powerpc/mm/book3s64/radix_tlb.c:1175:29: note: initialize the variable 'hend' to silence this warning
>                 unsigned long hstart, hend;
>                                           ^
>                                            = 0
> 2 errors generated.
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc: mm: radix_tlb: rearrange the if-else block
      https://git.kernel.org/powerpc/c/d78c8e32890ef7eca79ffd67c96022c7f9d8cce4

cheers