[PATCH] mm/swapfile:__swap_duplicate: drop redundant WRITE_ONCE on swap_map for err cases

[Barry Song <21cnbao@gmail.com>]

From: Barry Song <v-songbaohua@oppo.com>

The code is quite hard to read, we are still writing swap_map after
errors happen. Though the written value is as before,

 has_cache = count & SWAP_HAS_CACHE;
 count &= ~SWAP_HAS_CACHE;
 [snipped]
 WRITE_ONCE(p->swap_map[offset], count | has_cache);

It would be better to entirely drop the WRITE_ONCE for both
performance and readability.

Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 mm/swapfile.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 556ff7347d5f..17557003858c 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3320,6 +3320,9 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 	} else
 		err = -ENOENT;			/* unused swap entry */
 
+	if (err)
+		goto unlock_out;
+
 	WRITE_ONCE(p->swap_map[offset], count | has_cache);
 
 unlock_out:
-- 
2.34.1