swap: remove get/put_swap_device() in __swap_duplicate()

__swap_duplicate() is called by

- swap_shmem_alloc(): the folio in swap cache is locked.

- 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().

Link: https://lkml.kernel.org/r/20230529061355.125791-5-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Chris Li (Google) <chrisl@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2d264ef..bd03567 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3265,9 +3265,7 @@ 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);
@@ -3314,7 +3312,6 @@ 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;
 }