linux-kernel - Re: [PATCH v2] usb: dwc3: gadget: Prevent EPs resource conflict during StartTransfer

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Message-ID: <20251205011823.6ujxcjimlyetpjvj@synopsys.com>
Date: Fri, 5 Dec 2025 01:18:30 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Selvarasu Ganesan <selvarasu.g@...sung.com>
CC: Alan Stern <stern@...land.harvard.edu>,
        "gregkh@...uxfoundation.org"
	<gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org"
	<linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "jh0801.jung@...sung.com"
	<jh0801.jung@...sung.com>,
        "dh10.jung@...sung.com" <dh10.jung@...sung.com>,
        "naushad@...sung.com" <naushad@...sung.com>,
        "akash.m5@...sung.com"
	<akash.m5@...sung.com>,
        "h10.kim@...sung.com" <h10.kim@...sung.com>,
        "eomji.oh@...sung.com" <eomji.oh@...sung.com>,
        "alim.akhtar@...sung.com"
	<alim.akhtar@...sung.com>,
        "thiagu.r@...sung.com" <thiagu.r@...sung.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: gadget: Prevent EPs resource conflict
 during StartTransfer

On Fri, Dec 05, 2025, Thinh Nguyen wrote:
> On Thu, Dec 04, 2025, Selvarasu Ganesan wrote:
> > 
> > On 12/4/2025 7:21 AM, Thinh Nguyen wrote:
> > > At the moment, I can't think of a way to workaround for all cases. Let's
> > > just leave bulk streams alone for now. Until we have proper fixes to the
> > > gadget framework, let's just try the below.
> > >
> > 
> > 
> > Hi Thinh,
> > 
> > Thanks for the changes. We understand the given fix and have verified 
> > that the original issue is resolved, but a similar below warning appears 
> > again in `dwc3_gadget_ep_queue` when we run a long duration our test. 
> > And we confirmed this is not due to this new given changes.
> > 
> > This warning is caused by a race between `dwc3_gadget_ep_disable` and 
> > `dwc3_gadget_ep_queue` that manipulates `dep->flags`.
> > 
> > Please refer the below sequence for the reference.
> > 
> > The warning originates from a race condition between 
> > dwc3_gadget_ep_disable and dwc3_send_gadget_ep_cmd from 
> > dwc3_gadget_ep_queue that both manipulate dep->flags. Proper 
> > synchronization or a check is needed when masking (dep->flags &= mask) 
> > inside dwc3_gadget_ep_disable.
> > 
> 
> I was hoping that the dwc3_gadget_ep_queue() won't come early to run
> into this scenario. What I've provided will only mitigate and will not
> resolve for all cases. It seems adding more checks in dwc3 will be
> more messy.
> 
> Probably we should try rework the usb gadget framework instead of
> workaround the problem in dwc3. Here is a potential solution I'm
> thinking: introduce usb_ep_disable_with_flush().
> 

Actually, no. Let's just revert this:

b0d5d2a71641 ("usb: gadget: udc: core: Revise comments for USB ep enable/disable")

Reword the implementation in dwc3 and audit where usb_ep_disable() is used.

Thanks,
Thinh