From: Huang Ying <ying.huang@xxxxxxxxx> Subject: mm/swap_state.c: simplify total_swapcache_pages() with get_swap_device() 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. [ying.huang@xxxxxxxxx: fix bad swap file entry warning] Link: http://lkml.kernel.org/r/20190531024102.21723-1-ying.huang@xxxxxxxxx Link: http://lkml.kernel.org/r/20190527082714.12151-1-ying.huang@xxxxxxxxx Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Tested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Jérôme Glisse <jglisse@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Jan Kara <jack@xxxxxxx> Cc: Dave Jiang <dave.jiang@xxxxxxxxx> Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> Cc: Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/swap_state.c | 33 +++++++++++++++------------------ 1 file changed, 15 insertions(+), 18 deletions(-) --- a/mm/swap_state.c~mm-swap-simplify-total_swapcache_pages-with-get_swap_device +++ a/mm/swap_state.c @@ -73,23 +73,24 @@ 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) + swp_entry_t entry = swp_entry(i, 1); + + /* Avoid get_swap_device() to warn for bad swap entry */ + if (!swp_swap_info(entry)) + continue; + /* Prevent swapoff to free swapper_spaces */ + si = get_swap_device(entry); + 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 +612,16 @@ int init_swap_address_space(unsigned int 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, _
