linux-kernel - Re: New RCU related warning due to rcu_preempt

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Date:	Tue, 17 Apr 2012 17:36:59 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Dave Jones <davej@...hat.com>,
	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: New RCU related warning due to rcu_preempt_depth() changes

On Tue, Apr 17, 2012 at 5:05 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Tue, Apr 17, 2012 at 10:42:47AM +0200, Sasha Levin wrote:
>> Hi Paul,
>>
>> It looks like commit 7298b03 ("rcu: Move __rcu_read_lock() and
>> __rcu_read_unlock() to per-CPU variables") is causing the following
>> warning (I've added the extra fields on the second line):
>>
>> [   77.330920] BUG: sleeping function called from invalid context at
>> mm/memory.c:3933
>> [   77.336571] in_atomic(): 0, irqs_disabled(): 0, preempt count: 0,
>> preempt offset: 0, rcu depth: 1, pid: 5669, name: trinity
>> [   77.344135] no locks held by trinity/5669.
>> [   77.349644] Pid: 5669, comm: trinity Tainted: G        W
>> 3.4.0-rc3-next-20120417-sasha-dirty #83
>> [   77.354401] Call Trace:
>> [   77.355956]  [<ffffffff810e83f3>] __might_sleep+0x1f3/0x210
>> [   77.358811]  [<ffffffff81198eaf>] might_fault+0x2f/0xa0
>> [   77.361997]  [<ffffffff810e3228>] schedule_tail+0x88/0xb0
>> [   77.364671]  [<ffffffff826a01d3>] ret_from_fork+0x13/0x80
>>
>> As you can see, rcu_preempt_depth() returns 1 when running in that
>> context, which looks pretty odd.
>
> Ouch!!!
>
> So it looks like I missed a place where I need to save and restore
> the new per-CPU rcu_read_lock_nesting and rcu_read_unlock_special
> variables.  My (probably hopelessly naive) guess is that I need to add
> a rcu_switch_from() and rcu_switch_to() into schedule_tail(), but to
> make rcu_switch_from() take the task_struct pointer as an argument,
> passing in prev.
>
> Does this make sense, or am I still missing something here?

I've let the test run for a bit more, and it appears that I'm getting
this warning from lots of different sources, would this
schedule_tail() fix all of them?

Here's several traces for reference:

[  223.068875]  [<ffffffff810e83f3>] __might_sleep+0x1f3/0x210
[  223.070719]  [<ffffffff810b2a05>] close_files+0x1d5/0x220
[  223.072531]  [<ffffffff810b2830>] ? find_new_reaper+0x230/0x230
[  223.076325]  [<ffffffff810b4811>] put_files_struct+0x21/0x1b0
[  223.080649]  [<ffffffff8269eb20>] ? _raw_spin_unlock+0x30/0x60
[  223.084455]  [<ffffffff810b4a5d>] exit_files+0x4d/0x60
[  223.087967]  [<ffffffff810b51ac>] do_exit+0x28c/0x470
[  223.091369]  [<ffffffff810e44d1>] ? get_parent_ip+0x11/0x50
[  223.093190]  [<ffffffff810b5473>] do_group_exit+0xa3/0xe0
[  223.095061]  [<ffffffff810c4759>] get_signal_to_deliver+0x389/0x400
[  223.098400]  [<ffffffff8104bce2>] do_signal+0x42/0x120
[  223.100222]  [<ffffffff8104c4d7>] ? do_divide_error+0xa7/0xb0
[  223.102267]  [<ffffffff8269fa7f>] ? retint_signal+0x11/0x92
[  223.104145]  [<ffffffff8104be34>] do_notify_resume+0x54/0xa0
[  223.106033]  [<ffffffff8269fabb>] retint_signal+0x4d/0x92

[  176.217632]  [<ffffffff810e83f3>] __might_sleep+0x1f3/0x210
[  176.223583]  [<ffffffff81081b83>] do_page_fault+0x243/0x4f0
[  176.229932]  [<ffffffff811151ca>] ? __lock_release+0x1ba/0x1d0
[  176.233651]  [<ffffffff8269ec1b>] ? _raw_spin_unlock_irq+0x2b/0x80
[  176.239389]  [<ffffffff810e44d1>] ? get_parent_ip+0x11/0x50
[  176.242507]  [<ffffffff810e469e>] ? sub_preempt_count+0xae/0xe0
[  176.248795]  [<ffffffff8269ec41>] ? _raw_spin_unlock_irq+0x51/0x80
[  176.255454]  [<ffffffff81079e51>] do_async_page_fault+0x31/0xa0
[  176.260342]  [<ffffffff8269fcd5>] async_page_fault+0x25/0x30

[  173.587864]  [<ffffffff810e83f3>] __might_sleep+0x1f3/0x210
[  173.593134]  [<ffffffff811f5542>] ? __d_alloc+0x32/0x1a0
[  173.603730]  [<ffffffff811c0f8d>] kmem_cache_alloc+0x4d/0x160
[  173.604746]  [<ffffffff811f5e40>] ? __d_lookup_rcu+0x240/0x240
[  173.608932]  [<ffffffff811f5542>] __d_alloc+0x32/0x1a0
[  173.612444]  [<ffffffff811f56f3>] d_alloc+0x23/0x80
[  173.616887]  [<ffffffff811e773b>] __lookup_hash+0x9b/0x110
[  173.621488]  [<ffffffff811e77c4>] lookup_hash+0x14/0x20
[  173.624395]  [<ffffffff811ecc99>] do_unlinkat+0x79/0x1e0
[  173.626483]  [<ffffffff8269ec41>] ? _raw_spin_unlock_irq+0x51/0x80
[  173.632242]  [<ffffffff826a02e9>] ? sysret_check+0x22/0x5d
[  173.637884]  [<ffffffff8186db5e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[  173.642176]  [<ffffffff811ece51>] sys_unlink+0x11/0x20
[  173.645320]  [<ffffffff826a02bd>] system_call_fastpath+0x1a/0x1f
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