From ba81f83842549871cbd7226fc11530dc464500bb Mon Sep 17 00:00:00 2001 From: Huang Ying Date: Wed, 22 Feb 2017 15:45:46 -0800 Subject: [PATCH] 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 --- include/linux/swap_slots.h | 2 ++ mm/swap_slots.c | 2 +- mm/swap_state.c | 13 ++++++++++--- 3 files changed, 13 insertions(+), 4 deletions(-) diff --git a/include/linux/swap_slots.h b/include/linux/swap_slots.h index ba5623b27c60..6ef92d17633d 100644 --- a/include/linux/swap_slots.h +++ b/include/linux/swap_slots.h @@ -25,4 +25,6 @@ void reenable_swap_slots_cache_unlock(void); int enable_swap_slots_cache(void); int free_swap_slot(swp_entry_t entry); +extern bool swap_slot_cache_enabled; + #endif /* _LINUX_SWAP_SLOTS_H */ diff --git a/mm/swap_slots.c b/mm/swap_slots.c index ebf4f1cbac04..9b5bc86f96ad 100644 --- a/mm/swap_slots.c +++ b/mm/swap_slots.c @@ -36,7 +36,7 @@ static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots); static bool swap_slot_cache_active; -static bool swap_slot_cache_enabled; +bool swap_slot_cache_enabled; static bool swap_slot_cache_initialized; DEFINE_MUTEX(swap_slots_cache_mutex); /* Serialize swap slots cache enable/disable operations */ 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.