linux-kernel - Re: [PATCH v2] phy: use per-PHY lockdep keys

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Message-ID: <35789b5b-76a3-472f-adef-cc47f6d23dd4@linaro.org>
Date: Wed, 4 Jun 2025 17:26:03 +0200
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>,
 Abel Vesa <abel.vesa@...aro.org>
Cc: linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] phy: use per-PHY lockdep keys

On 30/05/2025 18:08, Dmitry Baryshkov wrote:
> If the PHY driver uses another PHY internally (e.g. in case of eUSB2,
> repeaters are represented as PHYs), then it would trigger the following
> lockdep splat because all PHYs use a single static lockdep key and thus
> lockdep can not identify whether there is a dependency or not and
> reports a false positive.
> 
> Make PHY subsystem use dynamic lockdep keys, assigning each driver a
> separate key. This way lockdep can correctly identify dependency graph
> between mutexes.
> 
>   ============================================
>   WARNING: possible recursive locking detected
>   6.15.0-rc7-next-20250522-12896-g3932f283970c #3455 Not tainted
>   --------------------------------------------
>   kworker/u51:0/78 is trying to acquire lock:
>   ffff0008116554f0 (&phy->mutex){+.+.}-{4:4}, at: phy_init+0x4c/0x12c
> 
>   but task is already holding lock:
>   ffff000813c10cf0 (&phy->mutex){+.+.}-{4:4}, at: phy_init+0x4c/0x12c
> 
>   other info that might help us debug this:
>    Possible unsafe locking scenario:
> 
>          CPU0
>          ----
>     lock(&phy->mutex);
>     lock(&phy->mutex);
> 
>    *** DEADLOCK ***
> 
>    May be due to missing lock nesting notation
> 
>   4 locks held by kworker/u51:0/78:
>    #0: ffff000800010948 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x18c/0x5ec
>    #1: ffff80008036bdb0 (deferred_probe_work){+.+.}-{0:0}, at: process_one_work+0x1b4/0x5ec
>    #2: ffff0008094ac8f8 (&dev->mutex){....}-{4:4}, at: __device_attach+0x38/0x188
>    #3: ffff000813c10cf0 (&phy->mutex){+.+.}-{4:4}, at: phy_init+0x4c/0x12c
> 
>   stack backtrace:
>   CPU: 0 UID: 0 PID: 78 Comm: kworker/u51:0 Not tainted 6.15.0-rc7-next-20250522-12896-g3932f283970c #3455 PREEMPT
>   Hardware name: Qualcomm CRD, BIOS 6.0.240904.BOOT.MXF.2.4-00528.1-HAMOA-1 09/ 4/2024
>   Workqueue: events_unbound deferred_probe_work_func
>   Call trace:
>    show_stack+0x18/0x24 (C)
>    dump_stack_lvl+0x90/0xd0
>    dump_stack+0x18/0x24
>    print_deadlock_bug+0x258/0x348
>    __lock_acquire+0x10fc/0x1f84
>    lock_acquire+0x1c8/0x338
>    __mutex_lock+0xb8/0x59c
>    mutex_lock_nested+0x24/0x30
>    phy_init+0x4c/0x12c
>    snps_eusb2_hsphy_init+0x54/0x1a0
>    phy_init+0xe0/0x12c
>    dwc3_core_init+0x450/0x10b4
>    dwc3_core_probe+0xce4/0x15fc
>    dwc3_probe+0x64/0xb0
>    platform_probe+0x68/0xc4
>    really_probe+0xbc/0x298
>    __driver_probe_device+0x78/0x12c
>    driver_probe_device+0x3c/0x160
>    __device_attach_driver+0xb8/0x138
>    bus_for_each_drv+0x84/0xe0
>    __device_attach+0x9c/0x188
>    device_initial_probe+0x14/0x20
>    bus_probe_device+0xac/0xb0
>    deferred_probe_work_func+0x8c/0xc8
>    process_one_work+0x208/0x5ec
>    worker_thread+0x1c0/0x368
>    kthread+0x14c/0x20c
>    ret_from_fork+0x10/0x20
> 
> Fixes: 3584f6392f09 ("phy: qcom: phy-qcom-snps-eusb2: Add support for eUSB2 repeater")
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> ---

Commented the wrong version:
In fact, other drivers were using sub-phys before:
./amlogic/phy-meson-axg-pcie.c
./amlogic/phy-meson-axg-mipi-dphy.c

(yeah I know, my bad !)

so it should be:
Fixes: e2463559ff1d ("phy: amlogic: Add Amlogic AXG PCIE PHY Driver")

With the Fixes changed:
Reviewed-by: Neil Armstrong <neil.armstrong@...aro.org>