On 07/23/2017 07:15 PM, Huang, Ying wrote: > Hi, Tim, > > Tim Chen <tim.c.c...@linux.intel.com> writes: > >> We will only reach the lock initialization code >> in alloc_swap_slot_cache when the cpu's swap_slots_cache's slots >> have not been allocated and swap_slots_cache has not been initialized >> previously. So the lock_initialized check is redundant and unnecessary. >> Remove lock_initialized flag from swap_slots_cache to save memory. > > Is there a race condition with CPU offline/online when preempt is enabled? > > CPU A CPU B > ----- ----- > get_swap_page() > get cache[B], cache[B]->slots != > NULL > preempted and moved to CPU A > be offlined > be onlined > alloc_swap_slot_cache() > mutex_lock(cache[B]->alloc_lock) > mutex_init(cache[B]->alloc_lock) > !!! > > The cache[B]->alloc_lock will be reinitialized when it is still held.
Looks like for this case the lock_initialized flag is still needed to prevent such races and prevent re-initialization of taken locks. Okay, let's scrap patch 2. Thanks. Tim
