Messages in this thread | | | Subject | Re: [PATCH 2/2] mm/swap: Remove lock_initialized flag from swap_slots_cache | From | Tim Chen <> | Date | Mon, 24 Jul 2017 09:54:50 -0700 |
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On 07/23/2017 07:15 PM, Huang, Ying wrote: > Hi, Tim, > > Tim Chen <tim.c.chen@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
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