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Date:	Fri, 14 Sep 2012 14:02:41 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kvm@...r.kernel.org
Subject: Re: memory-hotplug : possible circular locking dependency detected

At 09/13/2012 02:19 PM, Yasuaki Ishimatsu Wrote:
> When I offline a memory on linux-3.6-rc5, "possible circular
> locking dependency detected" messages are shown.
> Are the messages known problem?

It is a known problem, but it doesn't cause a deadlock.
There is 3 locks: memory hotplug's lock, memory hotplug
notifier's lock, and ksm_thread_mutex.

ksm_thread_mutex is locked when the memory is going offline
and is unlocked when the memory is offlined or the offlining
is cancelled. So we meet the warning messages. But it
doesn't cause deadlock, because we lock mem_hotplug_mutex
first.

Thanks
Wen Congyang

> 
> [  201.596363] Offlined Pages 32768
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> [  201.602143] 
> [  201.602150] ======================================================
> [  201.602153] [ INFO: possible circular locking dependency detected ]
> [  201.602157] 3.6.0-rc5 #1 Not tainted
> [  201.602159] -------------------------------------------------------
> [  201.602162] bash/2789 is trying to acquire lock:
> [  201.602164]  ((memory_chain).rwsem){.+.+.+}, at: [<ffffffff8109fe16>] __blocking_notifier_call_chain+0x66/0xd0
> [  201.602180] 
> [  201.602180] but task is already holding lock:
> [  201.602182]  (ksm_thread_mutex/1){+.+.+.}, at: [<ffffffff811b41fa>] ksm_memory_callback+0x3a/0xc0
> [  201.602194] 
> [  201.602194] which lock already depends on the new lock.
> [  201.602194] 
> [  201.602197] 
> [  201.602197] the existing dependency chain (in reverse order) is:
> [  201.602200] 
> [  201.602200] -> #1 (ksm_thread_mutex/1){+.+.+.}:
> [  201.602208]        [<ffffffff810dbee9>] validate_chain+0x6d9/0x7e0
> [  201.602214]        [<ffffffff810dc2e6>] __lock_acquire+0x2f6/0x4f0
> [  201.602219]        [<ffffffff810dc57d>] lock_acquire+0x9d/0x190
> [  201.602223]        [<ffffffff8166b4fc>] __mutex_lock_common+0x5c/0x420
> [  201.602229]        [<ffffffff8166ba2a>] mutex_lock_nested+0x4a/0x60
> [  201.602234]        [<ffffffff811b41fa>] ksm_memory_callback+0x3a/0xc0
> [  201.602239]        [<ffffffff81673447>] notifier_call_chain+0x67/0x150
> [  201.602244]        [<ffffffff8109fe2b>] __blocking_notifier_call_chain+0x7b/0xd0
> [  201.602250]        [<ffffffff8109fe96>] blocking_notifier_call_chain+0x16/0x20
> [  201.602255]        [<ffffffff8144c53b>] memory_notify+0x1b/0x20
> [  201.602261]        [<ffffffff81653c51>] offline_pages+0x1b1/0x470
> [  201.602267]        [<ffffffff811bfcae>] remove_memory+0x1e/0x20
> [  201.602273]        [<ffffffff8144c661>] memory_block_action+0xa1/0x190
> [  201.602278]        [<ffffffff8144c7c9>] memory_block_change_state+0x79/0xe0
> [  201.602282]        [<ffffffff8144c8f2>] store_mem_state+0xc2/0xd0
> [  201.602287]        [<ffffffff81436980>] dev_attr_store+0x20/0x30
> [  201.602293]        [<ffffffff812498d3>] sysfs_write_file+0xa3/0x100
> [  201.602299]        [<ffffffff811cba80>] vfs_write+0xd0/0x1a0
> [  201.602304]        [<ffffffff811cbc54>] sys_write+0x54/0xa0
> [  201.602309]        [<ffffffff81678529>] system_call_fastpath+0x16/0x1b
> [  201.602315] 
> [  201.602315] -> #0 ((memory_chain).rwsem){.+.+.+}:
> [  201.602322]        [<ffffffff810db7e7>] check_prev_add+0x527/0x550
> [  201.602326]        [<ffffffff810dbee9>] validate_chain+0x6d9/0x7e0
> [  201.602331]        [<ffffffff810dc2e6>] __lock_acquire+0x2f6/0x4f0
> [  201.602335]        [<ffffffff810dc57d>] lock_acquire+0x9d/0x190
> [  201.602340]        [<ffffffff8166c1a1>] down_read+0x51/0xa0
> [  201.602345]        [<ffffffff8109fe16>] __blocking_notifier_call_chain+0x66/0xd0
> [  201.602350]        [<ffffffff8109fe96>] blocking_notifier_call_chain+0x16/0x20
> [  201.602355]        [<ffffffff8144c53b>] memory_notify+0x1b/0x20
> [  201.602360]        [<ffffffff81653e67>] offline_pages+0x3c7/0x470
> [  201.602365]        [<ffffffff811bfcae>] remove_memory+0x1e/0x20
> [  201.602370]        [<ffffffff8144c661>] memory_block_action+0xa1/0x190
> [  201.602375]        [<ffffffff8144c7c9>] memory_block_change_state+0x79/0xe0
> [  201.602379]        [<ffffffff8144c8f2>] store_mem_state+0xc2/0xd0
> [  201.602385]        [<ffffffff81436980>] dev_attr_store+0x20/0x30
> [  201.602389]        [<ffffffff812498d3>] sysfs_write_file+0xa3/0x100
> [  201.602394]        [<ffffffff811cba80>] vfs_write+0xd0/0x1a0
> [  201.602398]        [<ffffffff811cbc54>] sys_write+0x54/0xa0
> [  201.602403]        [<ffffffff81678529>] system_call_fastpath+0x16/0x1b
> [  201.602408] 
> [  201.602408] other info that might help us debug this:
> [  201.602408] 
> [  201.602412]  Possible unsafe locking scenario:
> [  201.602412] 
> [  201.602414]        CPU0                    CPU1
> [  201.602417]        ----                    ----
> [  201.602419]   lock(ksm_thread_mutex/1);
> [  201.602425]                                lock((memory_chain).rwsem);
> [  201.602430]                                lock(ksm_thread_mutex/1);
> [  201.602435]   lock((memory_chain).rwsem);
> [  201.602440] 
> [  201.602440]  *** DEADLOCK ***
> [  201.602440] 
> [  201.602444] 6 locks held by bash/2789:
> [  201.602446]  #0:  (&buffer->mutex){+.+.+.}, at: [<ffffffff81249879>] sysfs_write_file+0x49/0x100
> [  201.602456]  #1:  (s_active#212){.+.+.+}, at: [<ffffffff812498b7>] sysfs_write_file+0x87/0x100
> [  201.602467]  #2:  (&mem->state_mutex){+.+.+.}, at: [<ffffffff8144c78e>] memory_block_change_state+0x3e/0xe0
> [  201.602477]  #3:  (mem_hotplug_mutex){+.+.+.}, at: [<ffffffff811bf867>] lock_memory_hotplug+0x17/0x40
> [  201.602487]  #4:  (pm_mutex){+.+.+.}, at: [<ffffffff811bf885>] lock_memory_hotplug+0x35/0x40
> [  201.602497]  #5:  (ksm_thread_mutex/1){+.+.+.}, at: [<ffffffff811b41fa>] ksm_memory_callback+0x3a/0xc0
> [  201.602508] 
> [  201.602508] stack backtrace:
> [  201.602512] Pid: 2789, comm: bash Not tainted 3.6.0-rc5 #1
> [  201.602515] Call Trace:
> [  201.602522]  [<ffffffff810da119>] print_circular_bug+0x109/0x110
> [  201.602527]  [<ffffffff810db7e7>] check_prev_add+0x527/0x550
> [  201.602532]  [<ffffffff810dbee9>] validate_chain+0x6d9/0x7e0
> [  201.602537]  [<ffffffff810dc2e6>] __lock_acquire+0x2f6/0x4f0
> [  201.602543]  [<ffffffff8101f7c3>] ? native_sched_clock+0x13/0x80
> [  201.602547]  [<ffffffff810dc57d>] lock_acquire+0x9d/0x190
> [  201.602553]  [<ffffffff8109fe16>] ? __blocking_notifier_call_chain+0x66/0xd0
> [  201.602558]  [<ffffffff8166c1a1>] down_read+0x51/0xa0
> [  201.602563]  [<ffffffff8109fe16>] ? __blocking_notifier_call_chain+0x66/0xd0
> [  201.602569]  [<ffffffff8109fe16>] __blocking_notifier_call_chain+0x66/0xd0
> [  201.602574]  [<ffffffff81186dc6>] ? next_online_pgdat+0x26/0x50
> [  201.602580]  [<ffffffff8109fe96>] blocking_notifier_call_chain+0x16/0x20
> [  201.602585]  [<ffffffff8144c53b>] memory_notify+0x1b/0x20
> [  201.602590]  [<ffffffff81653e67>] offline_pages+0x3c7/0x470
> [  201.602596]  [<ffffffff811bfcae>] remove_memory+0x1e/0x20
> [  201.602601]  [<ffffffff8144c661>] memory_block_action+0xa1/0x190
> [  201.602606]  [<ffffffff8166ba2a>] ? mutex_lock_nested+0x4a/0x60
> [  201.602611]  [<ffffffff8144c7c9>] memory_block_change_state+0x79/0xe0
> [  201.602617]  [<ffffffff8118f3ec>] ? might_fault+0x5c/0xb0
> [  201.602622]  [<ffffffff8144c8f2>] store_mem_state+0xc2/0xd0
> [  201.602627]  [<ffffffff812498b7>] ? sysfs_write_file+0x87/0x100
> [  201.602632]  [<ffffffff81436980>] dev_attr_store+0x20/0x30
> [  201.602636]  [<ffffffff812498d3>] sysfs_write_file+0xa3/0x100
> [  201.602641]  [<ffffffff811cba80>] vfs_write+0xd0/0x1a0
> [  201.602646]  [<ffffffff811cbc54>] sys_write+0x54/0xa0
> [  201.602652]  [<ffffffff81678529>] system_call_fastpath+0x16/0x1b
> 
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