Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Alexander Stein <alexander.stein@ew.tq-group.com>
To:     NXP Linux Team <linux-imx@nxp.com>,
        "A. Sverdlin" <alexander.sverdlin@siemens.com>
Cc:     Alexander Sverdlin <alexander.sverdlin@siemens.com>,
        Dong Aisheng <aisheng.dong@nxp.com>,
        Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>, linux-i2c@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] i2c: lpi2c: cache peripheral clock rate
Date:   Fri, 21 Apr 2023 15:48:59 +0200
Message-ID: <9272339.EvYhyI6sBW@steina-w>
Organization: TQ-Systems GmbH
In-Reply-To: <20230310130815.562418-1-alexander.sverdlin@siemens.com>
References: <20230310130815.562418-1-alexander.sverdlin@siemens.com>
MIME-Version: 1.0
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Precedence: bulk

Hi,

sorry for the delay.

Am Freitag, 10. M=E4rz 2023, 14:08:15 CEST schrieb A. Sverdlin:
> From: Alexander Sverdlin <alexander.sverdlin@siemens.com>
>=20
> One of the reasons to do it is to save some CPU cycles on cpu_freq_get()
> under mutex. The second reason if the (false-positive) lockdep splat caus=
ed
> by the recursive feature of the "prepare_lock" (one clock instance is I2C
> peripheral clock and another is pcf85063 RTC as clock provider):
>=20
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
> WARNING: possible circular locking dependency detected
> 5.15.71+... #1 Tainted: G           O
> ------------------------------------------------------
> fs-value/2332 is trying to acquire lock:
> ffff8000096cae08 (prepare_lock){+.+.}-{3:3}, at: clk_prepare_lock
>=20
> but task is already holding lock:
> ffff000011021100 (i2c_register_adapter){+.+.}-{3:3}, at:
> i2c_adapter_lock_bus
>=20
> which lock already depends on the new lock.
>=20
> the existing dependency chain (in reverse order) is:
>=20
> -> #2 (i2c_register_adapter){+.+.}-{3:3}:
>        lock_acquire
>        rt_mutex_lock_nested
>        i2c_adapter_lock_bus
>        i2c_transfer
>        regmap_i2c_read
>        _regmap_raw_read
>        _regmap_bus_read
>        _regmap_read
>        regmap_read
>        pcf85063_probe
>        i2c_device_probe
>        really_probe
>        __driver_probe_device
>        driver_probe_device
>        __device_attach_driver
>        bus_for_each_drv
>        __device_attach
>        device_initial_probe
>        bus_probe_device
>        device_add
>        device_register
>        i2c_new_client_device
>        of_i2c_register_devices
>        i2c_register_adapter
>        __i2c_add_numbered_adapter
>        i2c_add_adapter
>        lpi2c_imx_probe
>        platform_probe
>        really_probe
>        __driver_probe_device
>        driver_probe_device
>        __device_attach_driver
>        bus_for_each_drv
>        __device_attach
>        device_initial_probe
>        bus_probe_device
>        deferred_probe_work_func
>        process_one_work
>        worker_thread
>        kthread
>        ret_from_fork
>=20
> -> #1 (rtc_pcf85063:560:(&config->regmap)->lock){+.+.}-{3:3}:
>        lock_acquire
>        __mutex_lock
>        mutex_lock_nested
>        regmap_lock_mutex
>        regmap_read
>        pcf85063_clkout_recalc_rate
>        __clk_register
>        devm_clk_register
>        pcf85063_probe
>        i2c_device_probe
>        really_probe
>        __driver_probe_device
>        driver_probe_device
>        __device_attach_driver
>        bus_for_each_drv
>        __device_attach
>        device_initial_probe
>        bus_probe_device
>        device_add
>        device_register
>        i2c_new_client_device
>        of_i2c_register_devices
>        i2c_register_adapter
>        __i2c_add_numbered_adapter
>        i2c_add_adapter
>        lpi2c_imx_probe
>        platform_probe
>        really_probe
>        __driver_probe_device
>        driver_probe_device
>        __device_attach_driver
>        bus_for_each_drv
>        __device_attach
>        device_initial_probe
>        bus_probe_device
>        deferred_probe_work_func
>        process_one_work
>        worker_thread
>        kthread
>        ret_from_fork
>=20
> -> #0 (prepare_lock){+.+.}-{3:3}:
>        __lock_acquire
>        lock_acquire.part.0
>        lock_acquire
>        __mutex_lock
>        mutex_lock_nested
>        clk_prepare_lock
>        clk_get_rate
>        lpi2c_imx_xfer
>        __i2c_transfer
>        i2c_transfer
>        regmap_i2c_read
>        _regmap_raw_read
>        regmap_raw_read
>        regmap_bulk_read
>        at24_read
>        nvmem_reg_read
>        bin_attr_nvmem_read
>        sysfs_kf_bin_read
>        kernfs_fop_read_iter
>        new_sync_read
>        vfs_read
>        ksys_read
>        __arm64_sys_read
>        invoke_syscall
>        ...
>=20
> other info that might help us debug this:
>=20
> Chain exists of:
>   prepare_lock --> rtc_pcf85063:560:(&config->regmap)->lock -->
> i2c_register_adapter
>=20
>  Possible unsafe locking scenario:
>=20
>        CPU0                    CPU1
>        ----                    ----
>   lock(i2c_register_adapter);
>                              =20
> lock(rtc_pcf85063:560:(&config->regmap)->lock); lock(i2c_register_adapter=
);
>   lock(prepare_lock);
>=20
>  *** DEADLOCK ***
>=20
> 4 locks held by .../2332:
>  #0: ffff0000146eb288 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_read_iter
>  #1: ffff000010fe4400 (kn->active#72){.+.+}-{0:0}, at: kernfs_fop_read_it=
er
>  #2: ffff0000110168e8 (&at24->lock){+.+.}-{3:3}, at: at24_read
>  #3: ffff000011021100 (i2c_register_adapter){+.+.}-{3:3}, at:
> i2c_adapter_lock_bus
>=20
> stack backtrace:
> CPU: 1 PID: 2332 Comm: ... Tainted: G           O      5.15.71+... #1
> Hardware name: ... (DT)
> Call trace:
>  dump_backtrace
>  show_stack
>  dump_stack_lvl
>  dump_stack
>  print_circular_bug
>  check_noncircular
>  __lock_acquire
>  lock_acquire.part.0
>  lock_acquire
>  __mutex_lock
>  mutex_lock_nested
>  clk_prepare_lock
>  clk_get_rate
>  lpi2c_imx_xfer
>  __i2c_transfer
>  i2c_transfer
>  regmap_i2c_read
>  _regmap_raw_read
>  regmap_raw_read
>  regmap_bulk_read
>  at24_read
>  nvmem_reg_read
>  bin_attr_nvmem_read
>  sysfs_kf_bin_read
>  kernfs_fop_read_iter
>  new_sync_read
>  vfs_read
>  ksys_read
>  __arm64_sys_read
>  invoke_syscall
>  ...
>=20
> Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
> ---
>  drivers/i2c/busses/i2c-imx-lpi2c.c | 33 +++++++++++++++++++++++++++---
>  1 file changed, 30 insertions(+), 3 deletions(-)
>=20
> Changelog:
> v3: fixed build error reported by kernel test robot <lkp@intel.com>
>   =20
> https://lore.kernel.org/oe-kbuild-all/202303102010.pAv56wKs-lkp@intel.com/
> v2: added clk_notifier as Alexander suggested
>=20
> diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c
> b/drivers/i2c/busses/i2c-imx-lpi2c.c index 188f2a36d2fd6..5f1d1d4e018bd
> 100644
> --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> @@ -100,6 +100,8 @@ struct lpi2c_imx_struct {
>  	__u8			*rx_buf;
>  	__u8			*tx_buf;
>  	struct completion	complete;
> +	struct notifier_block	clk_change_nb;
> +	unsigned int		rate_per;
>  	unsigned int		msglen;
>  	unsigned int		delivered;
>  	unsigned int		block_data;
> @@ -198,24 +200,37 @@ static void lpi2c_imx_stop(struct lpi2c_imx_struct
> *lpi2c_imx) } while (1);
>  }
>=20
> +static int lpi2c_imx_clk_change_cb(struct notifier_block *nb,
> +				   unsigned long action, void *data)
> +{
> +	struct clk_notifier_data *ndata =3D data;
> +	struct lpi2c_imx_struct *lpi2c_imx =3D container_of(nb,
> +							  struct=20
lpi2c_imx_struct,
> +							 =20
clk_change_nb);
> +
> +	if (action & POST_RATE_CHANGE)
> +		lpi2c_imx->rate_per =3D ndata->new_rate;
> +
> +	return NOTIFY_OK;
> +}
> +
>  /* CLKLO =3D I2C_CLK_RATIO * CLKHI, SETHOLD =3D CLKHI, DATAVD =3D CLKHI/=
2 */
>  static int lpi2c_imx_config(struct lpi2c_imx_struct *lpi2c_imx)
>  {
>  	u8 prescale, filt, sethold, clkhi, clklo, datavd;
> -	unsigned int clk_rate, clk_cycle;
> +	unsigned int clk_cycle;
>  	enum lpi2c_imx_pincfg pincfg;
>  	unsigned int temp;
>=20
>  	lpi2c_imx_set_mode(lpi2c_imx);
>=20
> -	clk_rate =3D clk_get_rate(lpi2c_imx->clks[0].clk);
>  	if (lpi2c_imx->mode =3D=3D HS || lpi2c_imx->mode =3D=3D ULTRA_FAST)
>  		filt =3D 0;
>  	else
>  		filt =3D 2;
>=20
>  	for (prescale =3D 0; prescale <=3D 7; prescale++) {
> -		clk_cycle =3D clk_rate / ((1 << prescale) * lpi2c_imx-
>bitrate)
> +		clk_cycle =3D lpi2c_imx->rate_per / ((1 << prescale) *=20
lpi2c_imx->bitrate)
>  			    - 3 - (filt >> 1);
>  		clkhi =3D (clk_cycle + I2C_CLK_RATIO) / (I2C_CLK_RATIO + 1);
>  		clklo =3D clk_cycle - clkhi;
> @@ -588,6 +603,18 @@ static int lpi2c_imx_probe(struct platform_device
> *pdev) if (ret)
>  		return ret;
>=20
> +	lpi2c_imx->clk_change_nb.notifier_call =3D lpi2c_imx_clk_change_cb;
> +	ret =3D devm_clk_notifier_register(&pdev->dev, lpi2c_imx->clks[0].clk,
> +					 &lpi2c_imx->clk_change_nb);
> +	if (ret)
> +		return dev_err_probe(&pdev->dev, ret,
> +				     "can't register peripheral clock=20
notifier\n");
> +	lpi2c_imx->rate_per =3D clk_get_rate(lpi2c_imx->clks[0].clk);
> +	if (!lpi2c_imx->rate_per) {
> +		dev_err(&pdev->dev, "can't get I2C peripheral clock=20
rate\n");
> +		return -EINVAL;
> +	}
> +

I would switch the order of the calls to devm_clk_notifier_register() and=20
clk_get_rate(). AFAICS this looks like a possible lost update. The notifier=
=20
might change rate_per before the (old) value from clk_get_rate is actually=
=20
assigned.

With this change you fix the following call chain (from a kernel log)

[    4.562396]        clk_prepare_lock+0x48/0x9c
[    4.566740]        clk_get_rate+0x1c/0x74
[    4.570736]        lpi2c_imx_config+0x4c/0x190
[    4.575167]        lpi2c_imx_master_enable+0x54/0x128
[    4.580205]        lpi2c_imx_xfer+0x2c/0x3c8

Unfortuantely this was just hiding another call path from lpi2c_imx_xfer to=
=20
clk_bulk_prepare. Here is my kernel log:

[   22.264508] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
[   22.270697] WARNING: possible circular locking dependency detected
[   22.276893] 6.3.0-rc7-next-20230420+ #6 Not tainted
[   22.281782] ------------------------------------------------------
[   22.287968] kworker/2:3/93 is trying to acquire lock:
[   22.293034] ffff800009d38bf8 (prepare_lock){+.+.}-{3:3}, at:=20
clk_prepare_lock+0x48/0x9c
[   22.301095]=20
[   22.301095] but task is already holding lock:
[   22.306942] ffff0000039ab100 (i2c_register_adapter){+.+.}-{3:3}, at:=20
i2c_adapter_lock_bus+0x20/0x2c
[   22.316046]=20
[   22.316046] which lock already depends on the new lock.
[   22.316046]=20
[   22.324238]=20
[   22.324238] the existing dependency chain (in reverse order) is:
[   22.331727]=20
[   22.331727] -> #2 (i2c_register_adapter){+.+.}-{3:3}:
[   22.338295]        __lock_acquire+0x370/0x6e8
[   22.342674]        lock_acquire.part.0+0xcc/0x208
[   22.347399]        lock_acquire+0x94/0x14c
[   22.351509]        rt_mutex_lock_nested+0x5c/0x98
[   22.356235]        i2c_adapter_lock_bus+0x20/0x2c
[   22.360961]        i2c_transfer+0x80/0x114
[   22.365069]        regmap_i2c_read+0x5c/0xa0
[   22.369362]        _regmap_raw_read+0x110/0x2dc
[   22.373905]        _regmap_bus_read+0x40/0x74
[   22.378274]        _regmap_read+0x74/0x248
[   22.382393]        regmap_read+0x48/0x70
[   22.386337]        pcf85063_probe+0xf0/0x4f4
[   22.390640]        i2c_device_probe+0x100/0x2d4
[   22.395206]        call_driver_probe+0x28/0x15c
[   22.399750]        really_probe+0x180/0x320
[   22.403946]        __driver_probe_device+0x84/0x144
[   22.408837]        driver_probe_device+0x38/0x150
[   22.413554]        __device_attach_driver+0xcc/0x194
[   22.418532]        bus_for_each_drv+0x80/0xdc
[   22.422910]        __device_attach+0xa8/0x1f8
[   22.426545] systemd-journald[128]: Oldest entry in /var/log/journal/
e4579cc7db6747028247b9b859e132d6/system.joural is older than the configured=
=20
file retention duration (1month), suggesting rotation.
[   22.427278]        device_initial_probe+0x10/0x18
[   22.427290]        bus_probe_device+0xa4/0xa8
[   22.427299]        device_add+0x3b0/0x508
[   22.427311]        device_register+0x1c/0x28
[   22.427323]        i2c_new_client_device+0x1c8/0x2bc
[   22.427333]        of_i2c_register_device+0xb4/0xdc
[   22.427344]        of_i2c_register_devices+0x80/0x154
[   22.456329] systemd-journald[128]: /var/log/journal/
e4579cc7db6747028247b9b859e132d6/system.journal: Journal heaer limits reach=
ed=20
or header out-of-date, rotating.
[   22.458176]        i2c_register_adapter+0x184/0x4c8
[   22.458202]        __i2c_add_numbered_adapter+0x5c/0xa4
[   22.502097]        i2c_add_adapter+0xa0/0xcc
[   22.502122]        lpi2c_imx_probe+0x23c/0x350
[   22.502135]        platform_probe+0x64/0xfc
[   22.502146]        call_driver_probe+0x28/0x15c
[   22.502155]        really_probe+0x180/0x320
[   22.502164]        __driver_probe_device+0x84/0x144
[   22.502173]        driver_probe_device+0x38/0x150
[   22.502182]        __device_attach_driver+0xcc/0x194
[   22.502191]        bus_for_each_drv+0x80/0xdc
[   22.502204]        __device_attach+0xa8/0x1f8
[   22.502212]        device_initial_probe+0x10/0x18
[   22.502222]        bus_probe_device+0xa4/0xa8
[   22.502230]        deferred_probe_work_func+0xa0/0xf0
[   22.502239]        process_one_work+0x284/0x5b0
[   22.502252]        worker_thread+0x68/0x39c
[   22.502263]        kthread+0x104/0x108
[   22.502274]        ret_from_fork+0x10/0x20
[   22.502286]=20
[   22.502286] -> #1 (rtc_pcf85063:594:(&config->regmap)->lock){+.+.}-{3:3}:
[   22.502310]        __lock_acquire+0x370/0x6e8
[   22.502322]        lock_acquire.part.0+0xcc/0x208
[   22.502332]        lock_acquire+0x94/0x14c
[   22.502341]        __mutex_lock+0x9c/0x838
[   22.502353]        mutex_lock_nested+0x20/0x28
[   22.502364]        regmap_lock_mutex+0x10/0x18
[   22.502377]        regmap_read+0x38/0x70
[   22.502389]        pcf85063_clkout_recalc_rate+0x2c/0x78
[   22.502403]        __clk_core_init+0x46c/0x4e0
[   22.502417]        __clk_register+0x160/0x23c
[   22.502429]        devm_clk_register+0x58/0xb4
[   22.502441]        pcf85063_probe+0x238/0x4f4
[   22.502451]        i2c_device_probe+0x100/0x2d4
[   22.502465]        call_driver_probe+0x28/0x15c
[   22.502473]        really_probe+0x180/0x320
[   22.502482]        __driver_probe_device+0x84/0x144
[   22.502491]        driver_probe_device+0x38/0x150
[   22.502500]        __device_attach_driver+0xcc/0x194
[   22.502509]        bus_for_each_drv+0x80/0xdc
[   22.502521]        __device_attach+0xa8/0x1f8
[   22.502530]        device_initial_probe+0x10/0x18
[   22.502539]        bus_probe_device+0xa4/0xa8
[   22.502548]        device_add+0x3b0/0x508
[   22.502559]        device_register+0x1c/0x28
[   22.502570]        i2c_new_client_device+0x1c8/0x2bc
[   22.502580]        of_i2c_register_device+0xb4/0xdc
[  OK  ] Started Network Time Synchronization[   22.502589]       =20
of_i2c_register_devices+0x80/0x154
=2E[   22.502599]        i2c_register_adapter+0x184/0x4c8

[   22.502607]        __i2c_add_numbered_adapter+0x5c/0xa4
[   22.502616]        i2c_add_adapter+0xa0/0xcc
[   22.502624]        lpi2c_imx_probe+0x23c/0x350
[   22.502636]        platform_probe+0x64/0xfc
[   22.502646]        call_driver_probe+0x28/0x15c
[   22.502655]        really_probe+0x180/0x320
[   22.502663]        __driver_probe_device+0x84/0x144
[   22.502672]        driver_probe_device+0x38/0x150
[   22.502681]        __device_attach_driver+0xcc/0x194
[   22.502690]        bus_for_each_drv+0x80/0xdc
[   22.502702]        __device_attach+0xa8/0x1f8
[   22.502711]        device_initial_probe+0x10/0x18
[   22.502720]        bus_probe_device+0xa4/0xa8
[   22.502729]        deferred_probe_work_func+0xa0/0xf0
[   22.502738]        process_one_work+0x284/0x5b0
[   22.502749]        worker_thread+0x68/0x39c
[   22.502760]        kthread+0x104/0x108
[   22.502770]        ret_from_fork+0x10/0x20
[   22.502779]=20
[   22.502779] -> #0 (prepare_lock){+.+.}-{3:3}:
[   22.502799]        check_prev_add+0xb0/0xc80
[   22.502809]        validate_chain+0x444/0x510
[   22.502818]        __lock_acquire+0x370/0x6e8
[   22.502827]        lock_acquire.part.0+0xcc/0x208
[   22.502837]        lock_acquire+0x94/0x14c
[   22.502846]        __mutex_lock+0x9c/0x838
[   22.502857]        mutex_lock_nested+0x20/0x28
[   22.502867]        clk_prepare_lock+0x48/0x9c
[   22.502878]        clk_prepare+0x1c/0x3c
[   22.502890]        clk_bulk_prepare+0x48/0xcc
[   22.502899]        lpi2c_runtime_resume+0x30/0x84
[   22.502910]        pm_generic_runtime_resume+0x28/0x3c
[   22.502923]        __genpd_runtime_resume+0x2c/0xa0
[   22.502935]        genpd_runtime_resume+0xbc/0x308
[   22.502944]        __rpm_callback+0x44/0x19c
[   22.502953]        rpm_callback+0x64/0x70
[   22.502962]        rpm_resume+0x438/0x6d8
[   22.502970]        __pm_runtime_resume+0x54/0xb0
[   22.502978]        lpi2c_imx_master_enable+0x24/0x128
[   22.502989]        lpi2c_imx_xfer+0x2c/0x3c8
[   22.502999]        __i2c_transfer+0xe4/0x5a0
[   22.503008]        i2c_transfer+0x90/0x114
[   22.503016]        i2c_transfer_buffer_flags+0x58/0x84
[   22.503025]        regmap_i2c_write+0x1c/0x4c
[   22.503035]        _regmap_raw_write_impl+0x7dc/0x944
[   22.503044]        _regmap_bus_raw_write+0x5c/0x74
[   22.503052]        _regmap_write+0x64/0x238
[   22.503060]        _regmap_update_bits+0x100/0x11c
[   22.503069]        regmap_update_bits_base+0x60/0x90
[   22.503077]        pca953x_gpio_set_value+0x74/0x90
[   22.503088]        gpiod_set_raw_value_commit+0x6c/0x7c
[   22.503098]        gpiod_set_value_nocheck+0x68/0x70
[   22.503107]        gpiod_set_value_cansleep+0x3c/0xa8
[   22.503116]        gpio_led_set_blocking+0x54/0x7c
[   22.503128]        set_brightness_delayed+0x90/0xd8
[   22.503138]        process_one_work+0x284/0x5b0
[   22.503149]        worker_thread+0x68/0x39c
[   22.503160]        kthread+0x104/0x108
[   22.503169]        ret_from_fork+0x10/0x20
[   22.503179]=20
[   22.503179] other info that might help us debug this:
[   22.503179]=20
[   22.503183] Chain exists of:
[   22.503183]   prepare_lock --> rtc_pcf85063:594:(&config->regmap)->lock =
=2D->=20
i2c_register_adapter
[   22.503183]=20
[   22.503207]  Possible unsafe locking scenario:
[   22.503207]=20
[   22.503210]        CPU0                    CPU1
[   22.503213]        ----                    ----
[   22.503216]   lock(i2c_register_adapter);
[   22.503225]                                lock(rtc_pcf85063:594:(&confi=
g-
>regmap)->lock);
[   22.503235]                                lock(i2c_register_adapter);
[   22.503244]   lock(prepare_lock);
[   22.503253]=20
[   22.503253]  *** DEADLOCK ***

Now lpi2c_runtime_resume will call into clk_prepare() which also calls=20
clk_prepare_lock() (identical to clk_get_rate).

Best regards,
Alexader

>  	pm_runtime_set_autosuspend_delay(&pdev->dev, I2C_PM_TIMEOUT);
>  	pm_runtime_use_autosuspend(&pdev->dev);
>  	pm_runtime_get_noresume(&pdev->dev);


=2D-=20
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Amtsgericht M=FCnchen, HRB 105018
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