Yu Zhao <yuzhao@xxxxxxxxxx> writes:
> On Thu, Jan 13, 2022 at 04:01:31PM +0530, Aneesh Kumar K.V wrote:
>> Yu Zhao <yuzhao@xxxxxxxxxx> writes:
>>
>> > Add /sys/kernel/mm/lru_gen/enabled as a runtime kill switch.
>>
>>
>> Got the below lockdep warning while using the above kill/enable switch
>>
>>
>> [ 84.252952] ======================================================
>> [ 84.253012] WARNING: possible circular locking dependency detected
>> [ 84.253074] 5.16.0-rc8-16204-g1cdcf1120b31 #511 Not tainted
>> [ 84.253135] ------------------------------------------------------
>> [ 84.253194] bash/2862 is trying to acquire lock:
>> [ 84.253243] c0000000021ff740 (cgroup_mutex){+.+.}-{3:3}, at: store_enable+0x80/0x1510
>> [ 84.253340]
>> but task is already holding lock:
>> [ 84.253410] c000000002221348 (mem_hotplug_lock){++++}-{0:0}, at: mem_hotplug_begin+0x30/0x50
>> [ 84.253503]
>> which lock already depends on the new lock.
>>
>> [ 84.255933] Chain exists of:
>> cgroup_mutex --> cpu_hotplug_lock --> mem_hotplug_lock
>
> Thanks. Will reverse the order between mem_hotplug_lock and
> cgroup_mutex in the next spin.
It also needs the unlocked variant of static_key_enable/disable.
[ 71.204397][ T2819] bash/2819 is trying to acquire lock:
[ 71.204446][ T2819] c0000000020e5cd0 (cpu_hotplug_lock){++++}-{0:0}, at: static_key_disable+0x24/0x50
[ 71.204542][ T2819]
[ 71.204542][ T2819] but task is already holding lock:
[ 71.204613][ T2819] c0000000020e5cd0 (cpu_hotplug_lock){++++}-{0:0}, at: mem_hotplug_begin+0x20/0x50
[ 71.204710][ T2819]
[ 71.204710][ T2819] other info that might help us debug this:
[ 71.204787][ T2819] Possible unsafe locking scenario:
[ 71.204787][ T2819]
[ 71.204860][ T2819] CPU0
[ 71.204901][ T2819] ----
[ 71.204941][ T2819] lock(cpu_hotplug_lock);
[ 71.204998][ T2819] lock(cpu_hotplug_lock);
[ 71.205053][ T2819]
[ 71.205053][ T2819] *** DEADLOCK ***
-aneesh
