Commit e9a6effa authored by Huang Ying's avatar Huang Ying Committed by Linus Torvalds

mm, swap: fix false error message in __swp_swapcount()

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

Fixes: e8c26ab6 ("mm/swap: skip readahead for unreferenced swap slots")
Signed-off-by: default avatar"Huang, Ying" <>
Reported-by: default avatarChristian Kujau <>
Acked-by: default avatarMinchan Kim <>
Suggested-by: default avatarMinchan Kim <>
Cc: Tim Chen <>
Cc: Michal Hocko <>
Cc: Hugh Dickins <>
Cc: <>	[4.11+]
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent aa8d22a1
......@@ -559,6 +559,7 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
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;
bool do_poll = true, page_allocated;
......@@ -572,6 +573,8 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
end_offset = offset | mask;
if (!start_offset) /* First page is swap header. */
if (end_offset >= si->max)
end_offset = si->max - 1;
for (offset = start_offset; offset <= end_offset ; offset++) {
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