Re: Odroid XU4 deadlock

[Javier Martinez Canillas]

Hello Anand,

On 04/08/2016 09:51 AM, Anand Moon wrote:
> Hi All,
> 
> I am observing this deadlock or warning on my Odroid XU4.
> I thinks the is related to clk from exynos5_i2c_xfer .... clk_prepare_enable
> but I am not able to figure out which clk.
>

By reading your logs, it seems the problem is a possible ABBA deadlock since
the S3C RTC driver grabs the prepare_lock and then the regmap->lock, and the
CPUFreq driver leads to the locks being grabbed in the inverse order.

> [   11.640221] ======================================================
> [   11.646343] [ INFO: possible circular locking dependency detected ]
> [   11.652590] 4.6.0-rc2-xu4ml #35 Not tainted
> [   11.656749] -------------------------------------------------------
> [   11.662992] kworker/1:1/85 is trying to acquire lock:
> [   11.668010]  (prepare_lock){+.+...}, at: [<c05bfed8>]
> clk_prepare_lock+0x50/0xf8
> [   11.675375]
> [   11.675375] but task is already holding lock:
> [   11.681185]  (sec_core:428:(regmap)->lock){+.+...}, at:
> [<c0481aec>] regmap_read+0x2c/0x5c
> [   11.689417]
> [   11.689417] which lock already depends on the new lock.
> [   11.689417]
> [   11.697561]
> [   11.697561] the existing dependency chain (in reverse order) is:
> [   11.705008]
> [   11.705008] -> #1 (sec_core:428:(regmap)->lock){+.+...}:
> [   11.710467]        [<c0482d30>] regmap_update_bits_base+0x30/0x70
> [   11.716545]        [<c05c617c>] s2mps11_clk_prepare+0x30/0x38
> [   11.722262]        [<c05c01f0>] clk_core_prepare+0x98/0xbc
> [   11.727711]        [<c05c12bc>] clk_prepare+0x1c/0x2c
> [   11.732734]        [<c0556fe4>] s3c_rtc_probe+0x2d0/0x43c

the S3C RTC driver tries to prepare the RTC source clock S2MPS11_CLK_AP
and that leads to the prepare_lock to be held and then the regmap->lock
since s2mps11_clk_prepare() calls regmap_update_bits().

> [   11.738108]        [<c046b9fc>] platform_drv_probe+0x4c/0xb0
> [   11.743749]        [<c046a1fc>] driver_probe_device+0x20c/0x2b8
> [   11.749641]        [<c0468594>] bus_for_each_drv+0x60/0x94
> [   11.755103]        [<c0469f10>] __device_attach+0xb4/0x118
> [   11.760558]        [<c04693b4>] bus_probe_device+0x88/0x90
> [   11.766020]        [<c0469850>] deferred_probe_work_func+0x6c/0x9c
> [   11.772169]        [<c013b52c>] process_one_work+0x1a8/0x514
> [   11.777806]        [<c013b8d0>] worker_thread+0x38/0x56c
> [   11.783082]        [<c0141d14>] kthread+0xf4/0x10c
> [   11.787847]        [<c0107950>] ret_from_fork+0x14/0x24
> [   11.793050]
> [   11.793050] -> #0 (prepare_lock){+.+...}:
> [   11.797212]        [<c0768dd8>] mutex_lock_nested+0x78/0x4dc
> [   11.802845]        [<c05bfed8>] clk_prepare_lock+0x50/0xf8
> [   11.808304]        [<c05c19c4>] clk_unprepare+0x1c/0x2c
> [   11.813499]        [<c055d720>] exynos5_i2c_xfer+0x1dc/0x304

and here the locks are grabbed in the inverse order, since the regulator
driver uses regmap read (grabbing the regmap->lock) and then a clock is
prepared in exynos5_i2c_xfer.

> [   11.819129]        [<c0559620>] __i2c_transfer+0x13c/0x278
> [   11.824589]        [<c05597f0>] i2c_transfer+0x94/0xc4
> [   11.829701]        [<c04868f0>] regmap_i2c_read+0x48/0x64
> [   11.835074]        [<c0482048>] _regmap_raw_read+0xb4/0x114
> [   11.840630]        [<c04820cc>] _regmap_bus_read+0x24/0x58
> [   11.846084]        [<c0481a68>] _regmap_read+0x60/0xb8
> [   11.851201]        [<c0481afc>] regmap_read+0x3c/0x5c
> [   11.856224]        [<c03e2354>] regulator_get_voltage_sel_regmap+0x20/0x54
> [   11.863109]        [<c03dc5d4>] _regulator_get_voltage+0x20/0xb8
> [   11.863141]        [<c03df058>] _regulator_do_set_voltage+0x240/0x370
> [   11.863173]        [<c03df254>] regulator_set_voltage_unlocked+0xcc/0x230
> [   11.863205]        [<c03df3e0>] regulator_set_voltage+0x28/0x54
> [   11.863234]        [<c0478a94>] _set_opp_voltage+0x30/0x98
> [   11.863264]        [<c0479ba8>] dev_pm_opp_set_rate+0x1e0/0x540
> [   11.863337]        [<c0580824>] __cpufreq_driver_target+0x168/0x290
> [   11.863375]        [<c0583b48>] od_dbs_timer+0xdc/0x164
> [   11.863407]        [<c0584114>] dbs_work_handler+0x30/0x58
> [   11.863437]        [<c013b52c>] process_one_work+0x1a8/0x514
> [   11.863465]        [<c013b8d0>] worker_thread+0x38/0x56c
> [   11.863496]        [<c0141d14>] kthread+0xf4/0x10c
> [   11.863528]        [<c0107950>] ret_from_fork+0x14/0x24
> [   11.863538]
> [   11.863538] other info that might help us debug this:
> [   11.863538]
> [   11.863548]  Possible unsafe locking scenario:
> [   11.863548]
> [   11.863557]        CPU0                    CPU1
> [   11.863565]        ----                    ----
> [   11.863589]   lock(sec_core:428:(regmap)->lock);
> [   11.863612]                                lock(prepare_lock);
> [   11.863634]                                lock(sec_core:428:(regmap)->lock);
> [   11.863655]   lock(prepare_lock);
> [   11.863664]
> [   11.863664]  *** DEADLOCK ***
> [   11.863664]

I should take a look in deep to the regmap and clock subsystems to better
understand the issue on how to solve it. But AFAICT the problem is that
the prepare_lock is a global mutex and the same regmap is used for both
the s2mps11 clocks and regulators, so the ABBA deadlock described below
can happen.

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America