linux-kernel - [PATCH -mm] mm, swap: Fix bad swap file entry warning

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Date:   Fri, 31 May 2019 10:41:02 +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>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Michal Hocko <mhocko@...e.com>,
        Minchan Kim <minchan@...nel.org>,
        Hugh Dickins <hughd@...gle.com>
Subject: [PATCH -mm] mm, swap: Fix bad swap file entry warning

From: Huang Ying <ying.huang@...el.com>

Mike reported the following warning messages

  get_swap_device: Bad swap file entry 1400000000000001

This is produced by

- total_swapcache_pages()
  - get_swap_device()

Where get_swap_device() is used to check whether the swap device is
valid and prevent it from being swapoff if so.  But get_swap_device()
may produce warning message as above for some invalid swap devices.
This is fixed via calling swp_swap_info() before get_swap_device() to
filter out the swap devices that may cause warning messages.

Fixes: 6a946753dbe6 ("mm/swap_state.c: simplify total_swapcache_pages() with get_swap_device()")
Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Andrea Parri <andrea.parri@...rulasolutions.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Hugh Dickins <hughd@...gle.com>
---
 mm/swap_state.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index b84c58b572ca..62da25b7f2ed 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -76,8 +76,13 @@ unsigned long total_swapcache_pages(void)
 	struct swap_info_struct *si;
 
 	for (i = 0; i < MAX_SWAPFILES; i++) {
+		swp_entry_t entry = swp_entry(i, 1);
+
+		/* Avoid get_swap_device() to warn for bad swap entry */
+		if (!swp_swap_info(entry))
+			continue;
 		/* Prevent swapoff to free swapper_spaces */
-		si = get_swap_device(swp_entry(i, 1));
+		si = get_swap_device(entry);
 		if (!si)
 			continue;
 		nr = nr_swapper_spaces[i];
-- 
2.20.1