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

[Minas Harutyunyan <Minas.Harutyunyan@synopsys.com>]

Hi Marek,

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@samsung.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?
Or we can keep it as sanity solution to avoid any other possible cases?

>   			dwc2_hsotg_remove(hsotg);
>   			goto error_init;
>   		}
> @@ -593,7 +594,8 @@ static int dwc2_driver_probe(struct platform_device *dev)
>   	if (hsotg->params.activate_stm_id_vb_detection)
>   		regulator_disable(hsotg->usb33d);
>   error:
> -	dwc2_lowlevel_hw_disable(hsotg);
> +	if (hsotg->dr_mode != USB_DR_MODE_PERIPHERAL)
> +		dwc2_lowlevel_hw_disable(hsotg);
>   	return retval;
>   }
>   
> 

Thanks,
Minas