swap_cluster_info lockdep splat

[Minchan Kim]

Hi Huang,

With changing from bit lock to spinlock of swap_cluster_info, my zram
test failed with below message. It seems nested lock problem so need to
play with lockdep.

Thanks.

=============================================
[ INFO: possible recursive locking detected ]
4.10.0-rc8-next-20170214-zram #24 Not tainted
---------------------------------------------
as/6557 is trying to acquire lock:
 (&(&((cluster_info + ci)->lock))->rlock){+.+.-.}, at: [<ffffffff811ddd03>] cluster_list_add_tail.part.31+0x33/0x70

but task is already holding lock:
 (&(&((cluster_info + ci)->lock))->rlock){+.+.-.}, at: [<ffffffff811df2bb>] swapcache_free_entries+0x9b/0x330

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&(&((cluster_info + ci)->lock))->rlock);
  lock(&(&((cluster_info + ci)->lock))->rlock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by as/6557:
 #0:  (&(&cache->free_lock)->rlock){......}, at: [<ffffffff811c206b>] free_swap_slot+0x8b/0x110
 #1:  (&(&p->lock)->rlock){+.+.-.}, at: [<ffffffff811df295>] swapcache_free_entries+0x75/0x330
 #2:  (&(&((cluster_info + ci)->lock))->rlock){+.+.-.}, at: [<ffffffff811df2bb>] swapcache_free_entries+0x9b/0x330

stack backtrace:
CPU: 3 PID: 6557 Comm: as Not tainted 4.10.0-rc8-next-20170214-zram #24
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
Call Trace:
 dump_stack+0x85/0xc2
 __lock_acquire+0x15ea/0x1640
 lock_acquire+0x100/0x1f0
 ? cluster_list_add_tail.part.31+0x33/0x70
 _raw_spin_lock+0x38/0x50
 ? cluster_list_add_tail.part.31+0x33/0x70
 cluster_list_add_tail.part.31+0x33/0x70
 swapcache_free_entries+0x2f9/0x330
 free_swap_slot+0xf8/0x110
 swapcache_free+0x36/0x40
 delete_from_swap_cache+0x5f/0xa0
 try_to_free_swap+0x6e/0xa0
 free_pages_and_swap_cache+0x7d/0xb0
 tlb_flush_mmu_free+0x36/0x60
 tlb_finish_mmu+0x1c/0x50
 exit_mmap+0xc7/0x150
 mmput+0x51/0x110
 do_exit+0x2b2/0xc30
 ? trace_hardirqs_on_caller+0x129/0x1b0
 do_group_exit+0x50/0xd0
 SyS_exit_group+0x14/0x20
 entry_SYSCALL_64_fastpath+0x23/0xc6
RIP: 0033:0x2b9a2dbdf309
RSP: 002b:00007ffe71887528 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00002b9a2dbdf309
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00002b9a2ded8858 R08: 000000000000003c R09: 00000000000000e7
R10: ffffffffffffff60 R11: 0000000000000246 R12: 00002b9a2ded8858
R13: 00002b9a2dedde80 R14: 000000000255f770 R15: 0000000000000001