* Re: [linux-next:master 10668/10701] include/linux/pgtable.h:203:2: note: in expansion of macro 'pte_clear'
2020-05-21 18:10 ` [linux-next:master 10668/10701] include/linux/pgtable.h:203:2: note: in expansion of macro 'pte_clear' Andrew Morton
@ 2020-05-21 18:58 ` Mike Rapoport
0 siblings, 0 replies; 2+ messages in thread
From: Mike Rapoport @ 2020-05-21 18:58 UTC (permalink / raw)
To: Andrew Morton
Cc: kbuild test robot, kbuild-all, Linux Memory Management List,
James E.J. Bottomley, Helge Deller, linux-parisc
On Thu, May 21, 2020 at 11:10:13AM -0700, Andrew Morton wrote:
> On Thu, 21 May 2020 17:30:52 +0800 kbuild test robot <lkp@intel.com> wrote:
>
> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> > head: fb57b1fabcb28f358901b2df90abd2b48abc1ca8
> > commit: ef03574dee21524cbdbbf2af29fe06a62610570d [10668/10701] mm: introduce include/linux/pgtable.h
> > config: parisc-randconfig-r011-20200521 (attached as .config)
> > compiler: hppa-linux-gcc (GCC) 9.3.0
> > reproduce:
> > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > chmod +x ~/bin/make.cross
> > git checkout ef03574dee21524cbdbbf2af29fe06a62610570d
> > # save the attached .config to linux build tree
> > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=parisc
> >
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kbuild test robot <lkp@intel.com>
> >
> > All warnings (new ones prefixed by >>, old ones prefixed by <<):
> >
> > In file included from include/linux/pgtable.h:6,
> > from include/linux/mm.h:95,
> > from include/linux/pid_namespace.h:7,
> > from include/linux/ptrace.h:10,
> > from arch/parisc/kernel/asm-offsets.c:20:
> > include/linux/pgtable.h: In function 'pte_clear_not_present_full':
> > arch/parisc/include/asm/pgtable.h:96:9: warning: variable 'old_pte' set but not used [-Wunused-but-set-variable]
> > 96 | pte_t old_pte; | ^~~~~~~
> > arch/parisc/include/asm/pgtable.h:322:34: note: in expansion of macro 'set_pte_at'
> > 322 | #define pte_clear(mm, addr, xp) set_pte_at(mm, addr, xp, __pte(0))
> > | ^~~~~~~~~~
> > >> include/linux/pgtable.h:203:2: note: in expansion of macro 'pte_clear'
> > 203 | pte_clear(mm, address, ptep);
> > | ^~~~~~~~~
> > include/linux/pgtable.h: In function '__ptep_modify_prot_commit':
> > arch/parisc/include/asm/pgtable.h:96:9: warning: variable 'old_pte' set but not used [-Wunused-but-set-variable]
>
> I can't reproduce this. And I can't see anything in -mm whcih would
> have triggered this warning.
>
> arch/parisc/include/asm/pgtable.h has
>
> #define set_pte_at(mm, addr, ptep, pteval) \
> do { \
> pte_t old_pte; \
> unsigned long flags; \
> spin_lock_irqsave(pgd_spinlock((mm)->pgd), flags);\
> old_pte = *ptep; \
> set_pte(ptep, pteval); \
> purge_tlb_entries(mm, addr); \
> spin_unlock_irqrestore(pgd_spinlock((mm)->pgd), flags);\
> } while (0)
>
> and old_pte has been set-but-not-used for a long time.
>
> Obviously we can fix it, but I'm worried that parisc's set_pte_at() was
> previously unused and we've now done something to cause it to be used,
> so we're now running previously untested code.
I can reporduce it with
make W=1 ARCH=parisc CROSS_COMPILE=/opt/gcc-8.1.0-nolibc/hppa-linux/bin/hppa-linux-
on both the v5.7-rc6 and linux-next.
The only difference in the header names:
--- build-master.log 2020-05-21 21:44:03.064168815 +0300
+++ build-next.log 2020-05-21 21:44:52.372330747 +0300
@@ -2,25 +2,26 @@
GEN Makefile
CALL scripts/atomic/check-atomics.sh
CC arch/parisc/kernel/asm-offsets.s
-In file included from include/linux/mm.h:95,
+In file included from include/linux/pgtable.h:6,
+ from include/linux/mm.h:31,
from include/linux/pid_namespace.h:7,
from include/linux/ptrace.h:10,
from arch/parisc/kernel/asm-offsets.c:20:
-include/asm-generic/pgtable.h: In function 'pte_clear_not_present_full':
+include/linux/pgtable.h: In function 'pte_clear_not_present_full':
arch/parisc/include/asm/pgtable.h:96:9: warning: variable 'old_pte' set but not used [-Wunused-but-set-variable]
pte_t old_pte; \
^~~~~~~
arch/parisc/include/asm/pgtable.h:322:34: note: in expansion of macro 'set_pte_at'
#define pte_clear(mm, addr, xp) set_pte_at(mm, addr, xp, __pte(0))
^~~~~~~~~~
...
I think moving asm-generic/pgtable.h to linux/pgtable.h triggered the
"new warning" notification.
And the fix is obviously:
From 6de5f02d11fef8894836168c3e7bede05916d02d Mon Sep 17 00:00:00 2001
From: Mike Rapoport <rppt@linux.ibm.com>
Date: Thu, 21 May 2020 21:49:01 +0300
Subject: [PATCH] parisc: set_pte_at: remove unused old_pte variable.
kbuild test robot complains about unused variable old_pte in set_pte_at()
macro:
arch/parisc/include/asm/pgtable.h:96:9: warning: variable 'old_pte' set but not used [-Wunused-but-set-variable]
96 | pte_t old_pte; | ^~~~~~~
arch/parisc/include/asm/pgtable.h:322:34: note: in expansion of macro 'set_pte_at'
322 | #define pte_clear(mm, addr, xp) set_pte_at(mm, addr, xp, __pte(0))
Remove the old_pte variable.
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
arch/parisc/include/asm/pgtable.h | 2 --
1 file changed, 2 deletions(-)
diff --git a/arch/parisc/include/asm/pgtable.h b/arch/parisc/include/asm/pgtable.h
index 097d19007f2e..75cf84070fc9 100644
--- a/arch/parisc/include/asm/pgtable.h
+++ b/arch/parisc/include/asm/pgtable.h
@@ -93,10 +93,8 @@ static inline void purge_tlb_entries(struct mm_struct *mm, unsigned long addr)
#define set_pte_at(mm, addr, ptep, pteval) \
do { \
- pte_t old_pte; \
unsigned long flags; \
spin_lock_irqsave(pgd_spinlock((mm)->pgd), flags);\
- old_pte = *ptep; \
set_pte(ptep, pteval); \
purge_tlb_entries(mm, addr); \
spin_unlock_irqrestore(pgd_spinlock((mm)->pgd), flags);\
--
2.26.2
--
Sincerely yours,
Mike.
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