From: Sebastian Andrzej Siewior Date: Fri, 23 Jun 2017 11:43:30 +0200 Subject: [PATCH] mm, swap: 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. Signed-off-by: Sebastian Andrzej Siewior --- mm/swap_slots.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) --- a/mm/swap_slots.c +++ b/mm/swap_slots.c @@ -267,11 +267,11 @@ 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; } @@ -291,7 +291,6 @@ int free_swap_slot(swp_entry_t entry) direct_free: swapcache_free_entries(&entry, 1); } - put_cpu_var(swp_slots); return 0; }