linux-kernel - Lockdep broken on x1e80100 (was: Re: [PATCH v5 0/7] sm8550: Add support for eUSB2 repeater)

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Date: Tue, 25 Jun 2024 08:47:29 +0200
From: Johan Hovold <johan@...nel.org>
To: Abel Vesa <abel.vesa@...aro.org>,
	Neil Armstrong <neil.armstrong@...aro.org>
Cc: Andy Gross <agross@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Lee Jones <lee@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	"vkoul@...nel.org" <vkoul@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Johan Hovold <johan+linaro@...nel.org>,
	linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
	devicetree@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Lockdep broken on x1e80100 (was: Re: [PATCH v5 0/7] sm8550: Add
 support for eUSB2 repeater)

On Wed, Feb 08, 2023 at 09:01:53PM +0200, Abel Vesa wrote:
> This patchset adds support for the eUSB2 repeater found in pmic PM8550B,
> used along with SM8550. Since there is no dedicated generic framework
> for eUSB2 repeaters, the most appropriate subsystem to model it is the
> generic phy. This patchset also adds support for such repeater to the
> eUSB2 PHY found in SM8550. Basically, the eUSB2 PHY will have its own
> "phy" which is actually a repeater.

The decision to model the repeater as a PHY unfortunately breaks lockdep
as you now have functions like phy_init() calling phy_init() for a
second PHY (the repeater, see splat below).

As long as the locks are always taken in the same order there should be
no risk for a deadlock, but can you please verify that and add the
missing lockdep annotation so that lockdep can be used on platforms like
x1e80100 (e.g. to prevent further locking issues from being introduced)?

Johan


[    8.613248] ============================================
[    8.669073] WARNING: possible recursive locking detected
[    8.669074] 6.10.0-rc5 #122 Not tainted
[    8.669075] --------------------------------------------
[    8.669075] kworker/u50:0/77 is trying to acquire lock:
[    8.669076] ffff5cae8733ecf8 (&phy->mutex){+.+.}-{3:3}, at: phy_init+0x4c/0x12c
[    8.669087]
               but task is already holding lock:
[    8.669088] ffff5cae8a056cf8 (&phy->mutex){+.+.}-{3:3}, at: phy_init+0x4c/0x12c
[    8.669092]
               other info that might help us debug this:
[    8.669092]  Possible unsafe locking scenario:

[    8.669093]        CPU0
[    8.669093]        ----
[    8.669094]   lock(&phy->mutex);
[    8.669095]   lock(&phy->mutex);
[    8.669097]
                *** DEADLOCK ***

[    8.669097]  May be due to missing lock nesting notation

[    8.669097] 4 locks held by kworker/u50:0/77:
[    8.669099]  #0: ffff5cae80010948 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x1a4/0x638
[    8.669108]  #1: ffff800080333de0 (deferred_probe_work){+.+.}-{0:0}, at: process_one_work+0x1cc/0x638
[    8.669112]  #2: ffff5cae854038f8 (&dev->mutex){....}-{3:3}, at: __device_attach+0x38/0x1d4
[    8.669117]  #3: ffff5cae8a056cf8 (&phy->mutex){+.+.}-{3:3}, at: phy_init+0x4c/0x12c
[    8.669121]
               stack backtrace:
[    8.669122] CPU: 9 PID: 77 Comm: kworker/u50:0 Not tainted 6.10.0-rc5 #122
[    8.669124] Hardware name: Qualcomm CRD, BIOS 6.0.231221.BOOT.MXF.2.4-00348.1-HAMOA-1 12/21/2023
[    8.669125] Workqueue: events_unbound deferred_probe_work_func
[    8.669128] Call trace:
[    8.669129]  dump_backtrace+0x9c/0x11c
[    8.870384]  show_stack+0x18/0x24
[    8.870386]  dump_stack_lvl+0x90/0xd0
[    8.870391]  dump_stack+0x18/0x24
[    8.870393]  print_deadlock_bug+0x25c/0x348
[    8.870396]  __lock_acquire+0x10a4/0x2064
[    8.870399]  lock_acquire.part.0+0xc8/0x20c
[    8.870401]  lock_acquire+0x68/0x84
[    8.870403]  __mutex_lock+0x98/0x428
[    8.870407]  mutex_lock_nested+0x24/0x30
[    8.870410]  phy_init+0x4c/0x12c
[    8.870412]  qcom_snps_eusb2_hsphy_init+0x54/0x420 [phy_qcom_snps_eusb2]
[    8.870416]  phy_init+0xe0/0x12c
[    8.870418]  dwc3_core_init+0x484/0x1214
[    8.870421]  dwc3_probe+0xe54/0x171c
[    8.870424]  platform_probe+0x68/0xd8
[    8.870426]  really_probe+0xc0/0x388
[    8.870427]  __driver_probe_device+0x7c/0x160
[    8.870429]  driver_probe_device+0x40/0x114
[    8.870430]  __device_attach_driver+0xbc/0x158
[    8.870432]  bus_for_each_drv+0x84/0xe0
[    8.870433]  __device_attach+0xa8/0x1d4
[    8.870435]  device_initial_probe+0x14/0x20
[    8.870436]  bus_probe_device+0xb0/0xb4
[    8.870437]  deferred_probe_work_func+0xa0/0xf4
[    8.870439]  process_one_work+0x224/0x638
[    8.870441]  worker_thread+0x268/0x3a8
[    8.870442]  kthread+0x124/0x128
[    8.870443]  ret_from_fork+0x10/0x20