[patch 16/32] mm/debug_vm_pgtable: fix build failure with powerpc 8xx

From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, anshuman.khandual@arm.com,
	benh@kernel.crashing.org, christophe.leroy@csgroup.eu,
	mm-commits@vger.kernel.org, mpe@ellerman.id.au, paulus@samba.org,
	peterz@infradead.org, torvalds@linux-foundation.org,
	will@kernel.org
Subject: [patch 16/32] mm/debug_vm_pgtable: fix build failure with powerpc 8xx
Date: Thu, 25 Jun 2020 20:30:04 -0700	[thread overview]
Message-ID: <20200626033004.6lbFec3Ud%akpm@linux-foundation.org> (raw)
In-Reply-To: <20200625202807.b630829d6fa55388148bee7d@linux-foundation.org>

From: Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: mm/debug_vm_pgtable: fix build failure with powerpc 8xx

Since commit 9e343b467c70 ("READ_ONCE: Enforce atomicity for
{READ,WRITE}_ONCE() memory accesses"), READ_ONCE() cannot be used anymore
to read complex page table entries.  This leads to:

  CC      mm/debug_vm_pgtable.o
In file included from ./include/asm-generic/bug.h:5,
                 from ./arch/powerpc/include/asm/bug.h:109,
                 from ./include/linux/bug.h:5,
                 from ./include/linux/mmdebug.h:5,
                 from ./include/linux/gfp.h:5,
                 from mm/debug_vm_pgtable.c:13:
In function 'pte_clear_tests',
    inlined from 'debug_vm_pgtable' at mm/debug_vm_pgtable.c:363:2:
./include/linux/compiler.h:392:38: error: call to '__compiletime_assert_210' declared with attribute error: Unsupported access size for {READ,WRITE}_ONCE().
  392 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |                                      ^
./include/linux/compiler.h:373:4: note: in definition of macro '__compiletime_assert'
  373 |    prefix ## suffix();    \
      |    ^~~~~~
./include/linux/compiler.h:392:2: note: in expansion of macro '_compiletime_assert'
  392 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |  ^~~~~~~~~~~~~~~~~~~
./include/linux/compiler.h:405:2: note: in expansion of macro 'compiletime_assert'
  405 |  compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \
      |  ^~~~~~~~~~~~~~~~~~
./include/linux/compiler.h:291:2: note: in expansion of macro 'compiletime_assert_rwonce_type'
  291 |  compiletime_assert_rwonce_type(x);    \
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/debug_vm_pgtable.c:249:14: note: in expansion of macro 'READ_ONCE'
  249 |  pte_t pte = READ_ONCE(*ptep);
      |              ^~~~~~~~~
make[2]: *** [mm/debug_vm_pgtable.o] Error 1

Fix it by using the recently added ptep_get() helper.

Link: http://lkml.kernel.org/r/6ca8c972e6c920dc4ae0d4affbed9703afa4d010.1592490570.git.christophe.leroy@csgroup.eu
Fixes: 9e343b467c70 ("READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/debug_vm_pgtable.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/debug_vm_pgtable.c~mm-debug_vm_pgtable-fix-build-failure-with-powerpc-8xx
+++ a/mm/debug_vm_pgtable.c
@@ -246,13 +246,13 @@ static void __init pgd_populate_tests(st
 static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
 				   unsigned long vaddr)
 {
-	pte_t pte = READ_ONCE(*ptep);
+	pte_t pte = ptep_get(ptep);
 
 	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
 	set_pte_at(mm, vaddr, ptep, pte);
 	barrier();
 	pte_clear(mm, vaddr, ptep);
-	pte = READ_ONCE(*ptep);
+	pte = ptep_get(ptep);
 	WARN_ON(!pte_none(pte));
 }
 
_
