From f07e0f849a921ec8c0b509c8b8030455a2b21f7f Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Mon, 10 Jul 2017 15:49:29 -0700 Subject: mm/swap_slots.c: don't disable preemption while taking the per-CPU cache get_cpu_var() disables preemption and returns the per-CPU version of the variable. Disabling preemption is useful to ensure atomic access to the variable within the critical section. In this case however, after the per-CPU version of the variable is obtained the ->free_lock is acquired. For that reason it seems the raw accessor could be used. It only seems that ->slots_ret should be retested (because with disabled preemption this variable can not be set to NULL otherwise). This popped up during PREEMPT-RT testing because it tries to take spinlocks in a preempt disabled section. In RT, spinlocks can sleep. Link: http://lkml.kernel.org/r/20170623114755.2ebxdysacvgxzott@linutronix.de Signed-off-by: Sebastian Andrzej Siewior Acked-by: Michal Hocko Cc: Tim Chen Cc: Thomas Gleixner Cc: Ying Huang Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap_slots.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) (limited to 'mm/swap_slots.c') diff --git a/mm/swap_slots.c b/mm/swap_slots.c index 90c1032a8ac3..13a174006b91 100644 --- a/mm/swap_slots.c +++ b/mm/swap_slots.c @@ -273,11 +273,11 @@ int free_swap_slot(swp_entry_t entry) { struct swap_slots_cache *cache; - cache = &get_cpu_var(swp_slots); + cache = raw_cpu_ptr(&swp_slots); if (use_swap_slot_cache && cache->slots_ret) { spin_lock_irq(&cache->free_lock); /* Swap slots cache may be deactivated before acquiring lock */ - if (!use_swap_slot_cache) { + if (!use_swap_slot_cache || !cache->slots_ret) { spin_unlock_irq(&cache->free_lock); goto direct_free; } @@ -297,7 +297,6 @@ int free_swap_slot(swp_entry_t entry) direct_free: swapcache_free_entries(&entry, 1); } - put_cpu_var(swp_slots); return 0; } -- cgit v1.2.3