From: Huang Ying <huang.ying.caritas@gmail.com>
Date: Wed, 15 Nov 2017 17:33:15 -0800
Subject: mm, swap: fix false error message in __swp_swapcount()
Git-commit: e9a6effa500526e2a19d5ad042cb758b55b1ef93
Patch-mainline: v4.15-rc1
References: VM Functionality, bsc#1098043

[ Backport contains parts of 0bcac06f27d7528591c27ac2b093ccd71c5d0168 that
  introduce swp_swap_info() ]

When a page fault occurs for a swap entry, the physical swap readahead
(not the VMA base swap readahead) may readahead several swap entries
after the fault swap entry.  The readahead algorithm calculates some of
the swap entries to readahead via increasing the offset of the fault
swap entry without checking whether they are beyond the end of the swap
device and it relys on the __swp_swapcount() and swapcache_prepare() to
check it.  Although __swp_swapcount() checks for the swap entry passed
in, it will complain with the error message as follow for the expected
invalid swap entry.  This may make the end users confused.

  swap_info_get: Bad swap offset entry 0200f8a7

To fix the false error message, the swap entry checking is added in
swapin_readahead() to avoid to pass the out-of-bound swap entries and
the swap entry reserved for the swap header to __swp_swapcount() and
swapcache_prepare().

Link: http://lkml.kernel.org/r/20171102054225.22897-1-ying.huang@intel.com
Fixes: e8c26ab60598 ("mm/swap: skip readahead for unreferenced swap slots")
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reported-by: Christian Kujau <lists@nerdbynature.de>
Acked-by: Minchan Kim <minchan@kernel.org>
Suggested-by: Minchan Kim <minchan@kernel.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>	[4.11+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 include/linux/swap.h |    1 +
 mm/swap_state.c      |    3 +++
 mm/swapfile.c        |    5 +++++
 3 files changed, 9 insertions(+)

--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -427,6 +427,7 @@ extern int page_swapcount(struct page *)
 extern int __swp_swapcount(swp_entry_t entry);
 extern int swp_swapcount(swp_entry_t entry);
 extern struct swap_info_struct *page_swap_info(struct page *);
+extern struct swap_info_struct *swp_swap_info(swp_entry_t entry);
 extern bool reuse_swap_page(struct page *, int *);
 extern int try_to_free_swap(struct page *);
 struct backing_dev_info;
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -500,6 +500,7 @@ struct page *swapin_readahead(swp_entry_
 	unsigned long offset = entry_offset;
 	unsigned long start_offset, end_offset;
 	unsigned long mask;
+	struct swap_info_struct *si = swp_swap_info(entry);
 	struct blk_plug plug;
 
 	mask = swapin_nr_pages(offset) - 1;
@@ -511,6 +512,8 @@ struct page *swapin_readahead(swp_entry_
 	end_offset = offset | mask;
 	if (!start_offset)	/* First page is swap header. */
 		start_offset++;
+	if (end_offset >= si->max)
+		end_offset = si->max - 1;
 
 	blk_start_plug(&plug);
 	for (offset = start_offset; offset <= end_offset ; offset++) {
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3065,6 +3065,11 @@ int swapcache_prepare(swp_entry_t entry)
 	return __swap_duplicate(entry, SWAP_HAS_CACHE);
 }
 
+struct swap_info_struct *swp_swap_info(swp_entry_t entry)
+{
+	        return swap_info[swp_type(entry)];
+}
+
 struct swap_info_struct *page_swap_info(struct page *page)
 {
 	swp_entry_t swap = { .val = page_private(page) };