linux-kernel - Re: [PATCH v2] usb: dwc2: Fix error path in gadget registration

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Message-ID: <4741f20f-6e8e-157b-6ecb-828ad4423210@samsung.com>
Date:   Thu, 16 Jul 2020 14:33:21 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Felipe Balbi <balbi@...nel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2] usb: dwc2: Fix error path in gadget registration

Hi Minas,

On 16.07.2020 14:19, Minas Harutyunyan wrote:
> On 7/16/2020 4:09 PM, Marek Szyprowski wrote:
>> When gadget registration fails, one should not call usb_del_gadget_udc().
>> Ensure this by setting gadget->udc to NULL. Also in case of a failure
>> there is no need to disable low-level hardware, so return immiedetly
>> instead of jumping to error_init label.
>>
>> This fixes the following kernel NULL ptr dereference on gadget failure
>> (can be easily triggered with g_mass_storage without any module
>> parameters):
>>
>> dwc2 12480000.hsotg: dwc2_check_params: Invalid parameter besl=1
>> dwc2 12480000.hsotg: dwc2_check_params: Invalid parameter g_np_tx_fifo_size=1024
>> dwc2 12480000.hsotg: EPs: 16, dedicated fifos, 7808 entries in SPRAM
>> Mass Storage Function, version: 2009/09/11
>> LUN: removable file: (no medium)
>> no file given for LUN0
>> g_mass_storage 12480000.hsotg: failed to start g_mass_storage: -22
>> 8<--- cut here ---
>> Unable to handle kernel NULL pointer dereference at virtual address 00000104
>> pgd = (ptrval)
>> [00000104] *pgd=00000000
>> Internal error: Oops: 805 [#1] PREEMPT SMP ARM
>> Modules linked in:
>> CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.8.0-rc5 #3133
>> Hardware name: Samsung Exynos (Flattened Device Tree)
>> Workqueue: events deferred_probe_work_func
>> PC is at usb_del_gadget_udc+0x38/0xc4
>> LR is at __mutex_lock+0x31c/0xb18
>> ...
>> Process kworker/0:1 (pid: 12, stack limit = 0x(ptrval))
>> Stack: (0xef121db0 to 0xef122000)
>> ...
>> [<c076bf3c>] (usb_del_gadget_udc) from [<c0726bec>] (dwc2_hsotg_remove+0x10/0x20)
>> [<c0726bec>] (dwc2_hsotg_remove) from [<c0711208>] (dwc2_driver_probe+0x57c/0x69c)
>> [<c0711208>] (dwc2_driver_probe) from [<c06247c0>] (platform_drv_probe+0x6c/0xa4)
>> [<c06247c0>] (platform_drv_probe) from [<c0621df4>] (really_probe+0x200/0x48c)
>> [<c0621df4>] (really_probe) from [<c06221e8>] (driver_probe_device+0x78/0x1fc)
>> [<c06221e8>] (driver_probe_device) from [<c061fcd4>] (bus_for_each_drv+0x74/0xb8)
>> [<c061fcd4>] (bus_for_each_drv) from [<c0621b54>] (__device_attach+0xd4/0x16c)
>> [<c0621b54>] (__device_attach) from [<c0620c98>] (bus_probe_device+0x88/0x90)
>> [<c0620c98>] (bus_probe_device) from [<c06211b0>] (deferred_probe_work_func+0x3c/0xd0)
>> [<c06211b0>] (deferred_probe_work_func) from [<c0149280>] (process_one_work+0x234/0x7dc)
>> [<c0149280>] (process_one_work) from [<c014986c>] (worker_thread+0x44/0x51c)
>> [<c014986c>] (worker_thread) from [<c0150b1c>] (kthread+0x158/0x1a0)
>> [<c0150b1c>] (kthread) from [<c0100114>] (ret_from_fork+0x14/0x20)
>> Exception stack(0xef121fb0 to 0xef121ff8)
>> ...
>> ---[ end trace 9724c2fc7cc9c982 ]---
>>
>> While fixing this also fix the double call to dwc2_lowlevel_hw_disable()
>> if dr_mode is set to USB_DR_MODE_PERIPHERAL. In such case low-level
>> hardware is already disabled before calling usb_add_gadget_udc(). That
>> function correctly preserves low-level hardware state, there is no need
>> for the second unconditional dwc2_lowlevel_hw_disable() call.
>>
>> Fixes: 207324a321a8 ("usb: dwc2: Postponed gadget registration to the udc class driver")
>> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
>> ---
>>    drivers/usb/dwc2/platform.c | 4 +++-
>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/dwc2/platform.c b/drivers/usb/dwc2/platform.c
>> index cb8ddbd53718..db9fd4bd1a38 100644
>> --- a/drivers/usb/dwc2/platform.c
>> +++ b/drivers/usb/dwc2/platform.c
>> @@ -582,6 +582,7 @@ static int dwc2_driver_probe(struct platform_device *dev)
>>    	if (hsotg->gadget_enabled) {
>>    		retval = usb_add_gadget_udc(hsotg->dev, &hsotg->gadget);
>>    		if (retval) {
>> +			hsotg->gadget.udc = NULL;
> Consider your recently sent patch "[PATCH] usb: gadget: udc: Flush
> pending work also in error path", more probably it's not required,
> because root cause of observed dwc2 issue comes from udc.
> Am I wrong?

They are two independent issues, both fatal on my test system.

The first one (the lack of NULLing gadget->udc) can be easily triggered 
on any system. The latter one (lack of flush in UDC core) depends on the 
luck and memory layout on the test system.

Best regards

-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland