From: Huang Ying <[email protected]> total_swapcache_pages() may race with swapper_spaces[] allocation and freeing. Previously, this is protected with a swapper_spaces[] specific RCU mechanism. To simplify the logic/code complexity, it is replaced with get/put_swap_device(). The code line number is reduced too. Although not so important, the swapoff() performance improves too because one synchronize_rcu() call during swapoff() is deleted.
Signed-off-by: "Huang, Ying" <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Minchan Kim <[email protected]> Cc: Johannes Weiner <[email protected]> Cc: Tim Chen <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Jérôme Glisse <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Andrea Arcangeli <[email protected]> Cc: Yang Shi <[email protected]> Cc: David Rientjes <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Jan Kara <[email protected]> Cc: Dave Jiang <[email protected]> Cc: Daniel Jordan <[email protected]> Cc: Andrea Parri <[email protected]> --- mm/swap_state.c | 28 ++++++++++------------------ 1 file changed, 10 insertions(+), 18 deletions(-) diff --git a/mm/swap_state.c b/mm/swap_state.c index f509cdaa81b1..b84c58b572ca 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -73,23 +73,19 @@ unsigned long total_swapcache_pages(void) unsigned int i, j, nr; unsigned long ret = 0; struct address_space *spaces; + struct swap_info_struct *si; - rcu_read_lock(); for (i = 0; i < MAX_SWAPFILES; i++) { - /* - * The corresponding entries in nr_swapper_spaces and - * swapper_spaces will be reused only after at least - * one grace period. So it is impossible for them - * belongs to different usage. - */ - nr = nr_swapper_spaces[i]; - spaces = rcu_dereference(swapper_spaces[i]); - if (!nr || !spaces) + /* Prevent swapoff to free swapper_spaces */ + si = get_swap_device(swp_entry(i, 1)); + if (!si) continue; + nr = nr_swapper_spaces[i]; + spaces = swapper_spaces[i]; for (j = 0; j < nr; j++) ret += spaces[j].nrpages; + put_swap_device(si); } - rcu_read_unlock(); return ret; } @@ -611,20 +607,16 @@ int init_swap_address_space(unsigned int type, unsigned long nr_pages) mapping_set_no_writeback_tags(space); } nr_swapper_spaces[type] = nr; - rcu_assign_pointer(swapper_spaces[type], spaces); + swapper_spaces[type] = spaces; return 0; } void exit_swap_address_space(unsigned int type) { - struct address_space *spaces; - - spaces = swapper_spaces[type]; + kvfree(swapper_spaces[type]); nr_swapper_spaces[type] = 0; - rcu_assign_pointer(swapper_spaces[type], NULL); - synchronize_rcu(); - kvfree(spaces); + swapper_spaces[type] = NULL; } static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma, -- 2.20.1
