linux-kernel - [PATCH -V2 4/5] swap: remove get/put_swap_device() in __swap

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Date:   Mon, 22 May 2023 15:09:04 +0800
From:   Huang Ying <ying.huang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Huang Ying <ying.huang@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Minchan Kim <minchan@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Yang Shi <shy828301@...il.com>, Yu Zhao <yuzhao@...gle.com>
Subject: [PATCH -V2 4/5] swap: remove get/put_swap_device() in __swap_duplicate()

__swap_duplicate() is called by

- swap_shmem_alloc(): the page lock of the swap cache is held.

- copy_nonpresent_pte() -> swap_duplicate() and try_to_unmap_one() ->
  swap_duplicate(): the page table lock is held.

- __read_swap_cache_async() -> swapcache_prepare(): enclosed with
  get/put_swap_device() in __read_swap_cache_async() already.

So, it's safe to remove get/put_swap_device() in __swap_duplicate().

Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: Yang Shi <shy828301@...il.com>
Cc: Yu Zhao <yuzhao@...gle.com>
---
 mm/swapfile.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index e9cce775fb25..4dbaea64635d 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3264,9 +3264,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 	unsigned char has_cache;
 	int err;
 
-	p = get_swap_device(entry);
-	if (!p)
-		return -EINVAL;
+	p = swp_swap_info(entry);
 
 	offset = swp_offset(entry);
 	ci = lock_cluster_or_swap_info(p, offset);
@@ -3313,7 +3311,6 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 
 unlock_out:
 	unlock_cluster_or_swap_info(p, ci);
-	put_swap_device(p);
 	return err;
 }
 
-- 
2.39.2