kswapd using __this_cpu_add() in preemptible code

[Sergey Senozhatsky]

Hello gentlemen,

Commit 589a606f9539663f162e4a110d117527833b58a4 ("percpu: add preemption
checks to __this_cpu ops") added preempt check to used in __count_vm_events()
__this_cpu ops, causing the following kswapd warning:

 BUG: using __this_cpu_add() in preemptible [00000000] code: kswapd0/56
 caller is __this_cpu_preempt_check+0x2b/0x2d
 Call Trace:
 [<ffffffff813b8d4d>] dump_stack+0x4e/0x7a
 [<ffffffff8121366f>] check_preemption_disabled+0xce/0xdd
 [<ffffffff812136bb>] __this_cpu_preempt_check+0x2b/0x2d
 [<ffffffff810f622e>] inode_lru_isolate+0xed/0x197
 [<ffffffff810be43c>] list_lru_walk_node+0x7b/0x14c
 [<ffffffff810f6141>] ? iput+0x131/0x131
 [<ffffffff810f681f>] prune_icache_sb+0x35/0x4c
 [<ffffffff810e3951>] super_cache_scan+0xe3/0x143
 [<ffffffff810b1301>] shrink_slab_node+0x103/0x16f
 [<ffffffff810b19fd>] shrink_slab+0x75/0xe4
 [<ffffffff810b3f3d>] balance_pgdat+0x2fa/0x47f
 [<ffffffff810b4395>] kswapd+0x2d3/0x2fd
 [<ffffffff81068049>] ? __wake_up_sync+0xd/0xd
 [<ffffffff810b40c2>] ? balance_pgdat+0x47f/0x47f
 [<ffffffff81051e75>] kthread+0xd6/0xde
 [<ffffffff81051d9f>] ? kthread_create_on_node+0x162/0x162
 [<ffffffff813be5bc>] ret_from_fork+0x7c/0xb0
 [<ffffffff81051d9f>] ? kthread_create_on_node+0x162/0x162


list_lru_walk_node() seems to be the only place where __count_vm_events()
called with preemption enabled. remaining __count_vm_events() and
__count_vm_event() calls are done with preemption disabled (unless I
overlooked something).


	-ss
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