[Question] Is there race between swapoff and swapout

[Chen Wandun <chenwandun@xxxxxxxxxx>]

I analysied the code about swapoff and swapout, and I suspected there may be a race.
The kernel version is 4.14 stable.

CPU0						CPU1
swapoff						swap out
						add_to_swap
							get_swap_page
	......							get_swap_pages						
									spin_lock(&swap_avail_lock)
									get swap_info_struct
									spin_unlock(&swap_avail_lock)		
	spin_lock(&swap_avail_lock)									
	__def_from_avail_list(swap_info_struct)								
    	spin_unlock(&swap_avail_lock)					......	
	try_to_unuse  // unuse all slot
									/* get a free slot from swap_info_struct,
									 * and write data to slot later
									 */	
									scan_swap_map_slots
	free swap_info_struct
	.......

	
If CPU1 get the swap_info_struct first, then CPU0 delete it from list and
unuse all slot in swap_info_struct, before CPU0 free swap_info_struct CPU1
call scan_swap_map_slots to alloc a free slot.

I am not sure the analysis above is correct,
Please let me know if there is any mistake

Thanks
ChenWandun