Hi Tejun,
Sorry for late replay.
On 05/28/2014 11:48 PM, Tejun Heo wrote:
> (cc'ing Johannes for mm-foo)
>
> Hello,
>
> On Wed, May 28, 2014 at 06:06:34PM +0800, Gu Zheng wrote:
>> [ 2457.683370] inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-R} usage.
>> [ 2457.761540] kswapd2/1151 [HC0[0]:SC0[0]:HE1:SE1] takes:
>> [ 2457.824102] (&sig->group_rwsem){+++++?}, at: [<ffffffff81071864>] exit_signals+0x24/0x130
>> [ 2457.923538] {RECLAIM_FS-ON-W} state was registered at:
>> [ 2457.985055] [<ffffffff810bfc99>] mark_held_locks+0xb9/0x140
>> [ 2458.053976] [<ffffffff810c1e3a>] lockdep_trace_alloc+0x7a/0xe0
>> [ 2458.126015] [<ffffffff81194f47>] kmem_cache_alloc_trace+0x37/0x240
>> [ 2458.202214] [<ffffffff812c6e89>] flex_array_alloc+0x99/0x1a0
>> [ 2458.272175] [<ffffffff810da563>] cgroup_attach_task+0x63/0x430
>> [ 2458.344214] [<ffffffff810dcca0>] attach_task_by_pid+0x210/0x280
>> [ 2458.417294] [<ffffffff810dcd26>] cgroup_procs_write+0x16/0x20
>> [ 2458.488287] [<ffffffff810d8410>] cgroup_file_write+0x120/0x2c0
>> [ 2458.560320] [<ffffffff811b21a0>] vfs_write+0xc0/0x1f0
>> [ 2458.622994] [<ffffffff811b2bac>] SyS_write+0x4c/0xa0
>> [ 2458.684618] [<ffffffff815ec3c0>] tracesys+0xdd/0xe2
>> [ 2458.745214] irq event stamp: 49
>> [ 2458.782794] hardirqs last enabled at (49): [<ffffffff815e2b56>] _raw_spin_unlock_irqrestore+0x36/0x70
>> [ 2458.894388] hardirqs last disabled at (48): [<ffffffff815e337b>] _raw_spin_lock_irqsave+0x2b/0xa0
>> [ 2459.000771] softirqs last enabled at (0): [<ffffffff81059247>] copy_process.part.24+0x627/0x15f0
>> [ 2459.107161] softirqs last disabled at (0): [< (null)>] (null)
>> [ 2459.195852]
>> [ 2459.195852] other info that might help us debug this:
>> [ 2459.274024] Possible unsafe locking scenario:
>> [ 2459.274024]
>> [ 2459.344911] CPU0
>> [ 2459.374161] ----
>> [ 2459.403408] lock(&sig->group_rwsem);
>> [ 2459.448490] <Interrupt>
>> [ 2459.479825] lock(&sig->group_rwsem);
>> [ 2459.526979]
>> [ 2459.526979] *** DEADLOCK ***
>> [ 2459.526979]
>> [ 2459.597866] no locks held by kswapd2/1151.
>> [ 2459.646896]
>> [ 2459.646896] stack backtrace:
>> [ 2459.699049] CPU: 30 PID: 1151 Comm: kswapd2 Not tainted 3.10.39+ #4
>> [ 2459.774098] Hardware name: FUJITSU PRIMEQUEST2800E/SB, BIOS PRIMEQUEST 2000 Series BIOS Version 01.48 05/07/2014
>> [ 2459.895983] ffffffff82284bf0 ffff88085856bbf8 ffffffff815dbcf6 ffff88085856bc48
>> [ 2459.985003] ffffffff815d67c6 0000000000000000 ffff880800000001 ffff880800000001
>> [ 2460.074024] 000000000000000a ffff88085edc9600 ffffffff810be0e0 0000000000000009
>> [ 2460.163087] Call Trace:
>> [ 2460.192345] [<ffffffff815dbcf6>] dump_stack+0x19/0x1b
>> [ 2460.253874] [<ffffffff815d67c6>] print_usage_bug+0x1f7/0x208
>> [ 2460.399807] [<ffffffff810bfb5d>] mark_lock+0x21d/0x2a0
>> [ 2460.462369] [<ffffffff810c076a>] __lock_acquire+0x52a/0xb60
>> [ 2460.735516] [<ffffffff810c1592>] lock_acquire+0xa2/0x140
>> [ 2460.935691] [<ffffffff815e01e1>] down_read+0x51/0xa0
>> [ 2461.062888] [<ffffffff81071864>] exit_signals+0x24/0x130
>> [ 2461.127536] [<ffffffff81060d55>] do_exit+0xb5/0xa50
>> [ 2461.320433] [<ffffffff8108303b>] kthread+0xdb/0x100
>> [ 2461.532049] [<ffffffff815ec0ec>] ret_from_fork+0x7c/0xb0
>
> The lockdep warning is about threadgroup_lock being grabbed by kswapd
> which is depended upon during memory reclaim when the lock may be held
> by tasks which may wait on memory reclaim. From the backtrace, it
> looks like the right thing to do is marking the kswapd that it's no
> longer a memory reclaimer once before it starts exiting.
>
>> And when reference to the related code(kernel-3.10.y), it seems that cgroup_attach_task(thread-2,
>> attach kswapd) trigger kswapd(reclaim memory?) when trying to alloc memory(flex_array_alloc) under
>> the protection of sig->group_rwsem, but meanwhile the kswapd(thread-1) is in the exit routine
>> (because it was marked SHOULD STOP when offline pages completed), which needs to acquire
>> sig->group_rwsem in exit_signals(), so the deadlock occurs.
>>
>> thread-1 | thread-2
>> |
>> __offline_pages(): | system_call_fastpath()
>> |-> kswapd_stop(node); | |-> ......
>> |-> kthread_stop(kswapd) | |-> cgroup_file_write()
>> |-> set_bit(KTHREAD_SHOULD_STOP, &kthread->flags); | |-> ......
>> |-> wake_up_process(k) | |-> attach_task_by_pid()
>> | | |-> threadgroup_lock(tsk)
>> |<----------| | // Here, got the lock.
>> |-> kswapd() | |-> ...
>> |-> if (kthread_should_stop()) | |-> cgroup_attach_task()
>> return; | |-> flex_array_alloc()
>> | | |-> kzalloc()
>> |<----------| | |-> wait for kswapd to reclaim memory
>> |-> kthread() |
>> |-> do_exit(ret) |
>> |-> exit_signals() |
>> |-> threadgroup_change_begin(tsk) |
>> |-> down_read(&tsk->signal->group_rwsem) |
>> // Here, acquire the lock.
>>
>> If my analysis is correct, the latest kernel may have the same issue, though the flex_array was replaced
>> by list, but we still need to alloc memory(e.g. in find_css_set()), so the race may still occur.
>> Any comments about this? If I missed something, please correct me.:)
>
> Not sure whether this can actually happen but if so the right fix
> would be making thread-2 not wait for kswapd which is exiting and can
> no longer serve as memory reclaimer.
Thanks for your suggestion, I'll try this way if possible.
To Johannes:
Any comment about this issue and Tejun's suggestion?
Best regards,
Gu
>
> Thanks.
>
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