From ba81f83842549871cbd7226fc11530dc464500bb Mon Sep 17 00:00:00 2001 From: Huang Ying Date: Wed, 22 Feb 2017 15:45:46 -0800 Subject: mm/swap: skip readahead only when swap slot cache is enabled Because during swap off, a swap entry may have swap_map[] == SWAP_HAS_CACHE (for example, just allocated). If we return NULL in __read_swap_cache_async(), the swap off will abort. So when swap slot cache is disabled, (for swap off), we will wait for page to be put into swap cache in such race condition. This should not be a problem for swap slot cache, because swap slot cache should be drained after clearing swap_slot_cache_enabled. [ying.huang@intel.com: fix memory leak in __read_swap_cache_async()] Link: http://lkml.kernel.org/r/874lzt6znd.fsf@yhuang-dev.intel.com Link: http://lkml.kernel.org/r/5e2c5f6abe8e6eb0797408897b1bba80938e9b9d.1484082593.git.tim.c.chen@linux.intel.com Signed-off-by: "Huang, Ying" Signed-off-by: Tim Chen Cc: Aaron Lu Cc: Andi Kleen Cc: Andrea Arcangeli Cc: Christian Borntraeger Cc: Dave Hansen Cc: Hillf Danton Cc: Huang Ying Cc: Hugh Dickins Cc: Johannes Weiner Cc: Jonathan Corbet escreveu: Cc: Kirill A. Shutemov Cc: Michal Hocko Cc: Minchan Kim Cc: Rik van Riel Cc: Shaohua Li Cc: Vladimir Davydov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap_state.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) (limited to 'mm/swap_state.c') diff --git a/mm/swap_state.c b/mm/swap_state.c index e1f07cafecaa..473b71e052a8 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -324,9 +324,16 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, if (found_page) break; - /* Just skip read ahead for unused swap slot */ - if (!__swp_swapcount(entry)) - return NULL; + /* + * Just skip read ahead for unused swap slot. + * During swap_off when swap_slot_cache is disabled, + * we have to handle the race between putting + * swap entry in swap cache and marking swap slot + * as SWAP_HAS_CACHE. That's done in later part of code or + * else swap_off will be aborted if we return NULL. + */ + if (!__swp_swapcount(entry) && swap_slot_cache_enabled) + break; /* * Get a new page to read into from swap. -- cgit v1.2.3-59-g8ed1b