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Date: Wed, 29 Jun 2016 17:43:47 +0800
From: Peter Chen <hzpeterchen@gmail.com>
To: Stephen Boyd <stephen.boyd@linaro.org>
Cc: Peter Chen <peter.chen@nxp.com>, Felipe Balbi <balbi@kernel.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-usb@vger.kernel.org, Li Jun <jun.li@nxp.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] usb: otg-fsm: Cancel HNP polling work when not used
Message-ID: <20160629094347.GL25236@shlinux2>
References: <20160628011827.1688-1-stephen.boyd@linaro.org>
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On Mon, Jun 27, 2016 at 06:18:27PM -0700, Stephen Boyd wrote:
> We setup the HNP polling worker, but we never stop it. The OTG
> state machine can go round and round and keep reinitializing the
> worker even while it's actively running. That's bad, and debug
> objects catches it. Fix this by canceling the work when we leave
> the A_HOST or B_HOST states.
> 
> [otg_set_state]  Set state: a_wait_bcon
> usb 2-1: USB disconnect, device number 2
> [otg_statemachine]  quit statemachine, changed = 1
> [otg_set_state]  Set state: a_host
> <HNP Polling started>
> [otg_statemachine]  quit statemachine, changed = 1
> usb 2-1: new low-speed USB device number 3 using ci_hdrc
> usb 2-1: New USB device found, idVendor=03f0, idProduct=134a
> usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
> usb 2-1: Product: HP USB Optical Mouse
> usb 2-1: Manufacturer: PixArt
> input: PixArt HP USB Optical Mouse as /devices/platform/soc/f9a55000.usb/ci_hdrc.0/usb2/2-1/2-1:1.0/0003:03F0:134A.0002/input/input1
> hid-generic 0003:03F0:134A.0002: input: USB HID v1.11 Mouse [PixArt HP USB Optical Mouse] on usb-ci_hdrc.0-1/input0
> [otg_set_state]  Set state: a_wait_bcon
> usb 2-1: USB disconnect, device number 3
> [otg_statemachine]  quit statemachine, changed = 1
> [otg_set_state]  Set state: a_host
> <HNP Polling started>
> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 95 at lib/debugobjects.c:263 debug_print_object+0x98/0xc0
> ODEBUG: init active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x2c
> Modules linked in: phy_qcom_usb_hsic phy_qcom_usb_hs ci_hdrc_msm ci_hdrc
> CPU: 2 PID: 95 Comm: kworker/u8:1 Not tainted 4.7.0-rc1-00043-g1f22f3b65c44-dirty #442
> Hardware name: Qualcomm (Flattened Device Tree)
> Workqueue: ci_otg ci_otg_work [ci_hdrc]
> [<c031067c>] (unwind_backtrace) from [<c030cbf0>] (show_stack+0x20/0x24)
> [<c030cbf0>] (show_stack) from [<c060cec8>] (dump_stack+0x7c/0x9c)
> [<c060cec8>] (dump_stack) from [<c031f8a4>] (__warn+0xe4/0x110)
> [<c031f8a4>] (__warn) from [<c031f9a0>] (warn_slowpath_fmt+0x48/0x50)
> [<c031f9a0>] (warn_slowpath_fmt) from [<c06289c0>] (debug_print_object+0x98/0xc0)
> [<c06289c0>] (debug_print_object) from [<c0628bbc>] (__debug_object_init+0xcc/0x3bc)
> [<c0628bbc>] (__debug_object_init) from [<c0628ed0>] (debug_object_init+0x24/0x2c)
> [<c0628ed0>] (debug_object_init) from [<c037ceb0>] (init_timer_key+0x24/0x120)
> [<c037ceb0>] (init_timer_key) from [<c07b3f1c>] (otg_start_hnp_polling+0x7c/0xbc)
> [<c07b3f1c>] (otg_start_hnp_polling) from [<c074543c>] (otg_set_state+0x740/0xc20)
> [<c074543c>] (otg_set_state) from [<c0745d98>] (otg_statemachine+0x47c/0x4ac)
> [<c0745d98>] (otg_statemachine) from [<bf00c808>] (ci_otg_fsm_work+0x48/0x1a0 [ci_hdrc])
> [<bf00c808>] (ci_otg_fsm_work [ci_hdrc]) from [<bf007428>] (ci_otg_work+0xd4/0x218 [ci_hdrc])
> [<bf007428>] (ci_otg_work [ci_hdrc]) from [<c0338cac>] (process_one_work+0x154/0x4b4)
> [<c0338cac>] (process_one_work) from [<c033908c>] (worker_thread+0x38/0x4d0)
> [<c033908c>] (worker_thread) from [<c033f0a0>] (kthread+0xe8/0x104)
> [<c033f0a0>] (kthread) from [<c0308ed8>] (ret_from_fork+0x14/0x3c)
> 
> Cc: Li Jun <jun.li@nxp.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Fixes: ae57e97a9521 ("usb: common: otg-fsm: add HNP polling support")
> Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
> ---
>  drivers/usb/common/usb-otg-fsm.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/usb/common/usb-otg-fsm.c b/drivers/usb/common/usb-otg-fsm.c
> index 9059b7dc185e..73eec8c12235 100644
> --- a/drivers/usb/common/usb-otg-fsm.c
> +++ b/drivers/usb/common/usb-otg-fsm.c
> @@ -61,6 +61,18 @@ static int otg_set_protocol(struct otg_fsm *fsm, int protocol)
>  	return 0;
>  }
>  
> +static void otg_stop_hnp_polling(struct otg_fsm *fsm)
> +{
> +	/*
> +	 * The memory of host_req_flag should be allocated by
> +	 * controller driver, otherwise, hnp polling is not started.
> +	 */
> +	if (!fsm->host_req_flag)
> +		return;
> +
> +	cancel_delayed_work_sync(&fsm->hnp_polling_work);
> +}
> +
>  /* Called when leaving a state.  Do state clean up jobs here */
>  static void otg_leave_state(struct otg_fsm *fsm, enum usb_otg_state old_state)
>  {
> @@ -84,6 +96,7 @@ static void otg_leave_state(struct otg_fsm *fsm, enum usb_otg_state old_state)
>  		fsm->b_ase0_brst_tmout = 0;
>  		break;
>  	case OTG_STATE_B_HOST:
> +		otg_stop_hnp_polling(fsm);
>  		break;
>  	case OTG_STATE_A_IDLE:
>  		fsm->adp_prb = 0;
> @@ -97,6 +110,7 @@ static void otg_leave_state(struct otg_fsm *fsm, enum usb_otg_state old_state)
>  		fsm->a_wait_bcon_tmout = 0;
>  		break;
>  	case OTG_STATE_A_HOST:
> +		otg_stop_hnp_polling(fsm);
>  		otg_del_timer(fsm, A_WAIT_ENUM);
>  		break;
>  	case OTG_STATE_A_SUSPEND:
> -- 

It introduces circular locking after applying it, otg_statemachine calls
otg_leave_state, and otg_leave_state calls otg_statemachine again due
to flush work, see below dump:

I suggest moving initialization/flush hnp polling work to chipidea driver.

[  183.086987] ======================================================
[  183.093183] [ INFO: possible circular locking dependency detected ]
[  183.099471] 4.7.0-rc4-00012-gf1f333f-dirty #856 Not tainted
[  183.105059] -------------------------------------------------------
[  183.111341] kworker/0:2/114 is trying to acquire lock:
[  183.116492]  (&ci->fsm.lock){+.+.+.}, at: [<806118dc>]
otg_statemachine+0x20/0x470
[  183.124199] 
[  183.124199] but task is already holding lock:
[  183.130052]  ((&(&fsm->hnp_polling_work)->work)){+.+...}, at:
[<80140368>] process_one_work+0x128/0x418
[  183.139568] 
[  183.139568] which lock already depends on the new lock.
[  183.139568] 
[  183.147765] 
[  183.147765] the existing dependency chain (in reverse order) is:
[  183.155265] 
-> #1 ((&(&fsm->hnp_polling_work)->work)){+.+...}:
[  183.161371]        [<8013e97c>] flush_work+0x44/0x234
[  183.166469]        [<801411a8>] __cancel_work_timer+0x98/0x1c8
[  183.172347]        [<80141304>] cancel_delayed_work_sync+0x14/0x18
[  183.178570]        [<80610ef8>] otg_set_state+0x290/0xc54
[  183.184011]        [<806119d0>] otg_statemachine+0x114/0x470
[  183.189712]        [<8060a590>] ci_otg_fsm_work+0x40/0x190
[  183.195239]        [<806054d0>] ci_otg_work+0xcc/0x1e4
[  183.200430]        [<801403d4>] process_one_work+0x194/0x418
[  183.206136]        [<8014068c>] worker_thread+0x34/0x4fc
[  183.211489]        [<80146d08>] kthread+0xdc/0xf8
[  183.216238]        [<80108ab0>] ret_from_fork+0x14/0x24
[  183.221514] 
-> #0 (&ci->fsm.lock){+.+.+.}:
[  183.225880]        [<8016ff94>] lock_acquire+0x78/0x98
[  183.231062]        [<80947c18>] mutex_lock_nested+0x54/0x3ec
[  183.236773]        [<806118dc>] otg_statemachine+0x20/0x470
[  183.242388]        [<80611df4>] otg_hnp_polling_work+0xc8/0x1a4
[  183.248352]        [<801403d4>] process_one_work+0x194/0x418
[  183.254055]        [<8014068c>] worker_thread+0x34/0x4fc
[  183.259409]        [<80146d08>] kthread+0xdc/0xf8
[  183.264154]        [<80108ab0>] ret_from_fork+0x14/0x24
[  183.269424] 
[  183.269424] other info that might help us debug this:
[  183.269424] 
[  183.277451]  Possible unsafe locking scenario:
[  183.277451] 
[  183.283389]        CPU0                    CPU1
[  183.287931]        ----                    ----
[  183.292473]   lock((&(&fsm->hnp_polling_work)->work));
[  183.297665]                                lock(&ci->fsm.lock);
[  183.303639]
	lock((&(&fsm->hnp_polling_work)->work));
[  183.311347]   lock(&ci->fsm.lock);
[  183.314801] 
[  183.314801]  *** DEADLOCK ***
[  183.314801] 
[  183.320745] 2 locks held by kworker/0:2/114:
[  183.325028]  #0:  ("events"){.+.+.+}, at: [<80140368>]
process_one_work+0x128/0x418
[  183.332817]  #1:
((&(&fsm->hnp_polling_work)->work)){+.+...}, at: [<80140368>]
process_one_work+0x128/0x418
[  183.342772] 
[  183.342772] stack backtrace:
[  183.347160] CPU: 0 PID: 114 Comm: kworker/0:2 Not tainted
4.7.0-rc4-00012-gf1f333f-dirty #856
[  183.355699] Hardware name: Freescale i.MX6 SoloX (Device
		Tree)
[  183.361561] Workqueue: events otg_hnp_polling_work
[  183.366388] Backtrace: 
[  183.368891] [<8010d014>] (dump_backtrace) from [<8010d208>]
(show_stack+0x18/0x1c)
[  183.376479]  r6:600001d3 r5:00000000 r4:80f21d3c r3:00000002
[  183.382265] [<8010d1f0>] (show_stack) from [<803f158c>]
(dump_stack+0xb4/0xe8)
[  183.389521] [<803f14d8>] (dump_stack) from [<8016c2b4>]
(print_circular_bug+0x1d0/0x314)
[  183.397625]  r10:81760be8 r9:00000000 r8:bdb7bc00 r7:bdb7c0e0
r6:810c7074 r5:810ea174
[  183.405585]  r4:810c7074 r3:00000002
[  183.409231] [<8016c0e4>] (print_circular_bug) from
[<8016fa8c>] (__lock_acquire+0x196c/0x1ab4)
[  183.417857]  r10:80f21e1c r9:00000002 r8:00000001 r7:8174e47c
r6:00000002 r5:bdb7bc00
[  183.425814]  r4:00000026 r3:bdb7c0c0
[  183.429459] [<8016e120>] (__lock_acquire) from [<8016ff94>]
(lock_acquire+0x78/0x98)
[  183.437218]  r10:bdb701cc r9:bdbafeb0 r8:00001388 r7:00000001
r6:806118dc r5:60000153
[  183.445175]  r4:00000000
[  183.447758] [<8016ff1c>] (lock_acquire) from [<80947c18>]
(mutex_lock_nested+0x54/0x3ec)
[  183.455864]  r7:bdb7bc00 r6:8174e47c r5:806118dc r4:00000000
[  183.461645] [<80947bc4>] (mutex_lock_nested) from
[<806118dc>] (otg_statemachine+0x20/0x470)
[  183.470097]  r10:00000001 r9:bdbafeb0 r8:00001388 r7:bd3ef000
r6:00000009 r5:bdb701cc
[  183.478057]  r4:bdb70120
[  183.480641] [<806118bc>] (otg_statemachine) from [<80611df4>]
(otg_hnp_polling_work+0xc8/0x1a4)
[  183.489354]  r5:bdb70214 r4:00000000
[  183.493006] [<80611d2c>] (otg_hnp_polling_work) from
[<801403d4>] (process_one_work+0x194/0x418)
[  183.501805]  r8:00000000 r7:be7c4400 r6:be7c0ec0 r5:bdb70214
r4:bdb2d600
[  183.508650] [<80140240>] (process_one_work) from [<8014068c>]
(worker_thread+0x34/0x4fc)
[  183.516754]  r10:bdb2d600 r9:be7c0ec0 r8:80f02100 r7:be7c0ef4
r6:00000008 r5:bdb2d618
[  183.524712]  r4:be7c0ec0
[  183.527297] [<80140658>] (worker_thread) from [<80146d08>]
(kthread+0xdc/0xf8)
[  183.534534]  r10:00000000 r9:00000000 r8:00000000 r7:80140658
r6:bdb2d600 r5:bdb51000
[  183.542492]  r4:00000000
[  183.545081] [<80146c2c>] (kthread) from [<80108ab0>]
(ret_from_fork+0x14/0x24)
[  183.552317]  r7:00000000 r6:00000000 r5:80146c2c r4:bdb51000


-- 

Best Regards,
Peter Chen

From mboxrd@z Thu Jan  1 00:00:00 1970
From: hzpeterchen@gmail.com (Peter Chen)
Date: Wed, 29 Jun 2016 17:43:47 +0800
Subject: [PATCH] usb: otg-fsm: Cancel HNP polling work when not used
In-Reply-To: <20160628011827.1688-1-stephen.boyd@linaro.org>
References: <20160628011827.1688-1-stephen.boyd@linaro.org>
Message-ID: <20160629094347.GL25236@shlinux2>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Mon, Jun 27, 2016 at 06:18:27PM -0700, Stephen Boyd wrote:
> We setup the HNP polling worker, but we never stop it. The OTG
> state machine can go round and round and keep reinitializing the
> worker even while it's actively running. That's bad, and debug
> objects catches it. Fix this by canceling the work when we leave
> the A_HOST or B_HOST states.
> 
> [otg_set_state]  Set state: a_wait_bcon
> usb 2-1: USB disconnect, device number 2
> [otg_statemachine]  quit statemachine, changed = 1
> [otg_set_state]  Set state: a_host
> <HNP Polling started>
> [otg_statemachine]  quit statemachine, changed = 1
> usb 2-1: new low-speed USB device number 3 using ci_hdrc
> usb 2-1: New USB device found, idVendor=03f0, idProduct=134a
> usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
> usb 2-1: Product: HP USB Optical Mouse
> usb 2-1: Manufacturer: PixArt
> input: PixArt HP USB Optical Mouse as /devices/platform/soc/f9a55000.usb/ci_hdrc.0/usb2/2-1/2-1:1.0/0003:03F0:134A.0002/input/input1
> hid-generic 0003:03F0:134A.0002: input: USB HID v1.11 Mouse [PixArt HP USB Optical Mouse] on usb-ci_hdrc.0-1/input0
> [otg_set_state]  Set state: a_wait_bcon
> usb 2-1: USB disconnect, device number 3
> [otg_statemachine]  quit statemachine, changed = 1
> [otg_set_state]  Set state: a_host
> <HNP Polling started>
> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 95 at lib/debugobjects.c:263 debug_print_object+0x98/0xc0
> ODEBUG: init active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x2c
> Modules linked in: phy_qcom_usb_hsic phy_qcom_usb_hs ci_hdrc_msm ci_hdrc
> CPU: 2 PID: 95 Comm: kworker/u8:1 Not tainted 4.7.0-rc1-00043-g1f22f3b65c44-dirty #442
> Hardware name: Qualcomm (Flattened Device Tree)
> Workqueue: ci_otg ci_otg_work [ci_hdrc]
> [<c031067c>] (unwind_backtrace) from [<c030cbf0>] (show_stack+0x20/0x24)
> [<c030cbf0>] (show_stack) from [<c060cec8>] (dump_stack+0x7c/0x9c)
> [<c060cec8>] (dump_stack) from [<c031f8a4>] (__warn+0xe4/0x110)
> [<c031f8a4>] (__warn) from [<c031f9a0>] (warn_slowpath_fmt+0x48/0x50)
> [<c031f9a0>] (warn_slowpath_fmt) from [<c06289c0>] (debug_print_object+0x98/0xc0)
> [<c06289c0>] (debug_print_object) from [<c0628bbc>] (__debug_object_init+0xcc/0x3bc)
> [<c0628bbc>] (__debug_object_init) from [<c0628ed0>] (debug_object_init+0x24/0x2c)
> [<c0628ed0>] (debug_object_init) from [<c037ceb0>] (init_timer_key+0x24/0x120)
> [<c037ceb0>] (init_timer_key) from [<c07b3f1c>] (otg_start_hnp_polling+0x7c/0xbc)
> [<c07b3f1c>] (otg_start_hnp_polling) from [<c074543c>] (otg_set_state+0x740/0xc20)
> [<c074543c>] (otg_set_state) from [<c0745d98>] (otg_statemachine+0x47c/0x4ac)
> [<c0745d98>] (otg_statemachine) from [<bf00c808>] (ci_otg_fsm_work+0x48/0x1a0 [ci_hdrc])
> [<bf00c808>] (ci_otg_fsm_work [ci_hdrc]) from [<bf007428>] (ci_otg_work+0xd4/0x218 [ci_hdrc])
> [<bf007428>] (ci_otg_work [ci_hdrc]) from [<c0338cac>] (process_one_work+0x154/0x4b4)
> [<c0338cac>] (process_one_work) from [<c033908c>] (worker_thread+0x38/0x4d0)
> [<c033908c>] (worker_thread) from [<c033f0a0>] (kthread+0xe8/0x104)
> [<c033f0a0>] (kthread) from [<c0308ed8>] (ret_from_fork+0x14/0x3c)
> 
> Cc: Li Jun <jun.li@nxp.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Fixes: ae57e97a9521 ("usb: common: otg-fsm: add HNP polling support")
> Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
> ---
>  drivers/usb/common/usb-otg-fsm.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/usb/common/usb-otg-fsm.c b/drivers/usb/common/usb-otg-fsm.c
> index 9059b7dc185e..73eec8c12235 100644
> --- a/drivers/usb/common/usb-otg-fsm.c
> +++ b/drivers/usb/common/usb-otg-fsm.c
> @@ -61,6 +61,18 @@ static int otg_set_protocol(struct otg_fsm *fsm, int protocol)
>  	return 0;
>  }
>  
> +static void otg_stop_hnp_polling(struct otg_fsm *fsm)
> +{
> +	/*
> +	 * The memory of host_req_flag should be allocated by
> +	 * controller driver, otherwise, hnp polling is not started.
> +	 */
> +	if (!fsm->host_req_flag)
> +		return;
> +
> +	cancel_delayed_work_sync(&fsm->hnp_polling_work);
> +}
> +
>  /* Called when leaving a state.  Do state clean up jobs here */
>  static void otg_leave_state(struct otg_fsm *fsm, enum usb_otg_state old_state)
>  {
> @@ -84,6 +96,7 @@ static void otg_leave_state(struct otg_fsm *fsm, enum usb_otg_state old_state)
>  		fsm->b_ase0_brst_tmout = 0;
>  		break;
>  	case OTG_STATE_B_HOST:
> +		otg_stop_hnp_polling(fsm);
>  		break;
>  	case OTG_STATE_A_IDLE:
>  		fsm->adp_prb = 0;
> @@ -97,6 +110,7 @@ static void otg_leave_state(struct otg_fsm *fsm, enum usb_otg_state old_state)
>  		fsm->a_wait_bcon_tmout = 0;
>  		break;
>  	case OTG_STATE_A_HOST:
> +		otg_stop_hnp_polling(fsm);
>  		otg_del_timer(fsm, A_WAIT_ENUM);
>  		break;
>  	case OTG_STATE_A_SUSPEND:
> -- 

It introduces circular locking after applying it, otg_statemachine calls
otg_leave_state, and otg_leave_state calls otg_statemachine again due
to flush work, see below dump:

I suggest moving initialization/flush hnp polling work to chipidea driver.

[  183.086987] ======================================================
[  183.093183] [ INFO: possible circular locking dependency detected ]
[  183.099471] 4.7.0-rc4-00012-gf1f333f-dirty #856 Not tainted
[  183.105059] -------------------------------------------------------
[  183.111341] kworker/0:2/114 is trying to acquire lock:
[  183.116492]  (&ci->fsm.lock){+.+.+.}, at: [<806118dc>]
otg_statemachine+0x20/0x470
[  183.124199] 
[  183.124199] but task is already holding lock:
[  183.130052]  ((&(&fsm->hnp_polling_work)->work)){+.+...}, at:
[<80140368>] process_one_work+0x128/0x418
[  183.139568] 
[  183.139568] which lock already depends on the new lock.
[  183.139568] 
[  183.147765] 
[  183.147765] the existing dependency chain (in reverse order) is:
[  183.155265] 
-> #1 ((&(&fsm->hnp_polling_work)->work)){+.+...}:
[  183.161371]        [<8013e97c>] flush_work+0x44/0x234
[  183.166469]        [<801411a8>] __cancel_work_timer+0x98/0x1c8
[  183.172347]        [<80141304>] cancel_delayed_work_sync+0x14/0x18
[  183.178570]        [<80610ef8>] otg_set_state+0x290/0xc54
[  183.184011]        [<806119d0>] otg_statemachine+0x114/0x470
[  183.189712]        [<8060a590>] ci_otg_fsm_work+0x40/0x190
[  183.195239]        [<806054d0>] ci_otg_work+0xcc/0x1e4
[  183.200430]        [<801403d4>] process_one_work+0x194/0x418
[  183.206136]        [<8014068c>] worker_thread+0x34/0x4fc
[  183.211489]        [<80146d08>] kthread+0xdc/0xf8
[  183.216238]        [<80108ab0>] ret_from_fork+0x14/0x24
[  183.221514] 
-> #0 (&ci->fsm.lock){+.+.+.}:
[  183.225880]        [<8016ff94>] lock_acquire+0x78/0x98
[  183.231062]        [<80947c18>] mutex_lock_nested+0x54/0x3ec
[  183.236773]        [<806118dc>] otg_statemachine+0x20/0x470
[  183.242388]        [<80611df4>] otg_hnp_polling_work+0xc8/0x1a4
[  183.248352]        [<801403d4>] process_one_work+0x194/0x418
[  183.254055]        [<8014068c>] worker_thread+0x34/0x4fc
[  183.259409]        [<80146d08>] kthread+0xdc/0xf8
[  183.264154]        [<80108ab0>] ret_from_fork+0x14/0x24
[  183.269424] 
[  183.269424] other info that might help us debug this:
[  183.269424] 
[  183.277451]  Possible unsafe locking scenario:
[  183.277451] 
[  183.283389]        CPU0                    CPU1
[  183.287931]        ----                    ----
[  183.292473]   lock((&(&fsm->hnp_polling_work)->work));
[  183.297665]                                lock(&ci->fsm.lock);
[  183.303639]
	lock((&(&fsm->hnp_polling_work)->work));
[  183.311347]   lock(&ci->fsm.lock);
[  183.314801] 
[  183.314801]  *** DEADLOCK ***
[  183.314801] 
[  183.320745] 2 locks held by kworker/0:2/114:
[  183.325028]  #0:  ("events"){.+.+.+}, at: [<80140368>]
process_one_work+0x128/0x418
[  183.332817]  #1:
((&(&fsm->hnp_polling_work)->work)){+.+...}, at: [<80140368>]
process_one_work+0x128/0x418
[  183.342772] 
[  183.342772] stack backtrace:
[  183.347160] CPU: 0 PID: 114 Comm: kworker/0:2 Not tainted
4.7.0-rc4-00012-gf1f333f-dirty #856
[  183.355699] Hardware name: Freescale i.MX6 SoloX (Device
		Tree)
[  183.361561] Workqueue: events otg_hnp_polling_work
[  183.366388] Backtrace: 
[  183.368891] [<8010d014>] (dump_backtrace) from [<8010d208>]
(show_stack+0x18/0x1c)
[  183.376479]  r6:600001d3 r5:00000000 r4:80f21d3c r3:00000002
[  183.382265] [<8010d1f0>] (show_stack) from [<803f158c>]
(dump_stack+0xb4/0xe8)
[  183.389521] [<803f14d8>] (dump_stack) from [<8016c2b4>]
(print_circular_bug+0x1d0/0x314)
[  183.397625]  r10:81760be8 r9:00000000 r8:bdb7bc00 r7:bdb7c0e0
r6:810c7074 r5:810ea174
[  183.405585]  r4:810c7074 r3:00000002
[  183.409231] [<8016c0e4>] (print_circular_bug) from
[<8016fa8c>] (__lock_acquire+0x196c/0x1ab4)
[  183.417857]  r10:80f21e1c r9:00000002 r8:00000001 r7:8174e47c
r6:00000002 r5:bdb7bc00
[  183.425814]  r4:00000026 r3:bdb7c0c0
[  183.429459] [<8016e120>] (__lock_acquire) from [<8016ff94>]
(lock_acquire+0x78/0x98)
[  183.437218]  r10:bdb701cc r9:bdbafeb0 r8:00001388 r7:00000001
r6:806118dc r5:60000153
[  183.445175]  r4:00000000
[  183.447758] [<8016ff1c>] (lock_acquire) from [<80947c18>]
(mutex_lock_nested+0x54/0x3ec)
[  183.455864]  r7:bdb7bc00 r6:8174e47c r5:806118dc r4:00000000
[  183.461645] [<80947bc4>] (mutex_lock_nested) from
[<806118dc>] (otg_statemachine+0x20/0x470)
[  183.470097]  r10:00000001 r9:bdbafeb0 r8:00001388 r7:bd3ef000
r6:00000009 r5:bdb701cc
[  183.478057]  r4:bdb70120
[  183.480641] [<806118bc>] (otg_statemachine) from [<80611df4>]
(otg_hnp_polling_work+0xc8/0x1a4)
[  183.489354]  r5:bdb70214 r4:00000000
[  183.493006] [<80611d2c>] (otg_hnp_polling_work) from
[<801403d4>] (process_one_work+0x194/0x418)
[  183.501805]  r8:00000000 r7:be7c4400 r6:be7c0ec0 r5:bdb70214
r4:bdb2d600
[  183.508650] [<80140240>] (process_one_work) from [<8014068c>]
(worker_thread+0x34/0x4fc)
[  183.516754]  r10:bdb2d600 r9:be7c0ec0 r8:80f02100 r7:be7c0ef4
r6:00000008 r5:bdb2d618
[  183.524712]  r4:be7c0ec0
[  183.527297] [<80140658>] (worker_thread) from [<80146d08>]
(kthread+0xdc/0xf8)
[  183.534534]  r10:00000000 r9:00000000 r8:00000000 r7:80140658
r6:bdb2d600 r5:bdb51000
[  183.542492]  r4:00000000
[  183.545081] [<80146c2c>] (kthread) from [<80108ab0>]
(ret_from_fork+0x14/0x24)
[  183.552317]  r7:00000000 r6:00000000 r5:80146c2c r4:bdb51000


-- 

Best Regards,
Peter Chen