From: Huang Ying huang.ying.caritas@gmail.com Subject: 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 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 ---

mm/swap_state.c | 3 +++ 1 file changed, 3 insertions(+)

diff -puN mm/swap_state.c~mm-swap-fix-false-error-message-in-__swp_swapcount mm/swap_state.c --- a/mm/swap_state.c~mm-swap-fix-false-error-message-in-__swp_swapcount +++ a/mm/swap_state.c @@ -559,6 +559,7 @@ 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; bool do_poll = true, page_allocated;

@@ -572,6 +573,8 @@ 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++) { _