[PATCH] mm/swapfile: mm/swapfile: fix swapoff vs. software dirty bits

[Martin Schwidefsky <schwidefsky@de.ibm.com>]

Fixes a regression introduced with commit 179ef71cbc085252
"mm: save soft-dirty bits on swapped pages"

The maybe_same_pte() function is used to match a swap pte independent
of the swap software dirty bit set with pte_swp_mksoft_dirty().

For CONFIG_HAVE_ARCH_SOFT_DIRTY=y but CONFIG_MEM_SOFT_DIRTY=n the
software dirty bit may be set but maybe_same_pte() will not recognize
a software dirty swap pte. Due to this a 'swapoff -a' will hang.

The straightforward solution is to replace CONFIG_MEM_SOFT_DIRTY
with HAVE_ARCH_SOFT_DIRTY in maybe_same_pte().

Cc: linux-mm@kvack.org
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.cz>
Reported-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
 mm/swapfile.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5887731..bf7da58 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1113,7 +1113,7 @@ unsigned int count_swap_pages(int type, int free)
 
 static inline int maybe_same_pte(pte_t pte, pte_t swp_pte)
 {
-#ifdef CONFIG_MEM_SOFT_DIRTY
+#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
 	/*
 	 * When pte keeps soft dirty bit the pte generated
 	 * from swap entry does not has it, still it's same
-- 
1.9.1

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