linux-kernel - [PATCH v1 2/5] mm: ptdump: Fix build failure

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Date:   Thu, 15 Apr 2021 17:18:15 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Steven Price <steven.price@....com>, akpm@...ux-foundation.org
Cc:     linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, x86@...nel.org, linux-mm@...ck.org
Subject: [PATCH v1 2/5] mm: ptdump: Fix build failure

	  CC      mm/ptdump.o
	In file included from <command-line>:
	mm/ptdump.c: In function 'ptdump_pte_entry':
	././include/linux/compiler_types.h:320:38: error: call to '__compiletime_assert_207' declared with attribute error: Unsupported access size for {READ,WRITE}_ONCE().
	  320 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
	      |                                      ^
	././include/linux/compiler_types.h:301:4: note: in definition of macro '__compiletime_assert'
	  301 |    prefix ## suffix();    \
	      |    ^~~~~~
	././include/linux/compiler_types.h:320:2: note: in expansion of macro '_compiletime_assert'
	  320 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
	      |  ^~~~~~~~~~~~~~~~~~~
	./include/asm-generic/rwonce.h:36:2: note: in expansion of macro 'compiletime_assert'
	   36 |  compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \
	      |  ^~~~~~~~~~~~~~~~~~
	./include/asm-generic/rwonce.h:49:2: note: in expansion of macro 'compiletime_assert_rwonce_type'
	   49 |  compiletime_assert_rwonce_type(x);    \
	      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	mm/ptdump.c:114:14: note: in expansion of macro 'READ_ONCE'
	  114 |  pte_t val = READ_ONCE(*pte);
	      |              ^~~~~~~~~
	make[2]: *** [mm/ptdump.o] Error 1

READ_ONCE() cannot be used for reading PTEs. Use ptep_get()
instead. See commit 481e980a7c19 ("mm: Allow arches to provide ptep_get()")
and commit c0e1c8c22beb ("powerpc/8xx: Provide ptep_get() with 16k pages")
for details.

Fixes: 30d621f6723b ("mm: add generic ptdump")
Cc: Steven Price <steven.price@....com>
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 mm/ptdump.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/ptdump.c b/mm/ptdump.c
index 4354c1422d57..da751448d0e4 100644
--- a/mm/ptdump.c
+++ b/mm/ptdump.c
@@ -111,7 +111,7 @@ static int ptdump_pte_entry(pte_t *pte, unsigned long addr,
 			    unsigned long next, struct mm_walk *walk)
 {
 	struct ptdump_state *st = walk->private;
-	pte_t val = READ_ONCE(*pte);
+	pte_t val = ptep_get(pte);
 
 	if (st->effective_prot)
 		st->effective_prot(st, 4, pte_val(val));
-- 
2.25.0