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From: John Stultz <john.stultz@linaro.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: fei.yang@intel.com, Felipe Balbi <balbi@kernel.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	andrzej.p@collabora.com,
	Vincent Pelletier <plr.vincent@gmail.com>,
	Linux USB List <linux-usb@vger.kernel.org>,
	lkml <linux-kernel@vger.kernel.org>, Josh Gao <jmgao@google.com>,
	Alistair Strachan <astrachan@google.com>,
	Shen Jing <jingx.shen@intel.com>
Subject: Re: [PATCH V2] usb: gadget: f_fs: don't free buffer prematurely
Date: Wed, 20 Mar 2019 09:55:22 -0700	[thread overview]
Message-ID: <CALAqxLUdNe5PUnqM8MBdQaGkMU0QGuDjpWL0VeSCH_fx2jWGWg@mail.gmail.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1903201247570.1538-100000@iolanthe.rowland.org>

On Wed, Mar 20, 2019 at 9:52 AM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Wed, 20 Mar 2019, John Stultz wrote:
>
> > Hey Fei,
> >   So while this patch does resolve the issues I was seeing with
> > mainline kernels and recent changes to adbd, Josh pointed out that it
> > wouldn't resolve the issues I was seeing with older kernels which is
> > slightly different (but still related to aio usage).
> >
> > On the older kernels I'm hitting scheduling while atomic on reboot,
> > which seems to be due to ffs_aio_cancel() taking a spinlock then
> > calling usb_ep_dequeue() which might sleep.
> >
> > It seems a fix for this was tried earlier with d52e4d0c0c428 ("usb:
> > gadget: ffs: Fix BUG when userland exits with submitted AIO
> > transfers") which was then reverted by a9c859033f6e.
> >
> > Elsewhere it seems the ffs driver takes effort to drop any locks
> > before calling usb_ep_dequeue(), so this seems like that should be
> > addressed, but it also seems like recent change to the dwc3 driver has
> > been made to avoid sleeping in that path (see fec9095bdef4 ("usb:
> > dwc3: gadget: remove wait_end_transfer")), which may be why I'm not
> > seeing the problem with mainline (and your patch here, of coarse).
> > But that also doesn't clarify if its still a potential issue w/
> > non-dwc3 platforms.
> >
> > So for older kernels, do you have a suggestion of which approach is
> > advised?  Does usb_ep_dequeue need to avoid sleeping or do we need to
> > rework the ffs_aio_cancel logic?
>
> usb_ep_dequeue can be called in interrupt context, meaning it is never
> allowed to sleep.  This is mentioned in the kerneldoc:

Thanks for the clarification! Sorry I didn't see the kernel doc!
-john

  reply	other threads:[~2019-03-20 16:55 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-20  5:32 [PATCH V2] usb: gadget: f_fs: don't free buffer prematurely fei.yang
2019-03-20  5:56 ` Josh Gao
2019-03-20  5:59   ` Josh Gao
2019-03-20 17:30     ` Yang, Fei
2019-03-20 16:40 ` John Stultz
2019-03-20 16:52   ` Alan Stern
2019-03-20 16:55     ` John Stultz [this message]
2019-03-20 18:21   ` John Stultz
2019-04-02  3:26     ` John Stultz
2019-04-24 16:50       ` Greg KH
2019-04-25  3:53         ` John Stultz
2019-04-25 16:01           ` Yang, Fei
2019-04-25 16:19             ` John Stultz
2019-03-20 23:28   ` Yang, Fei
2019-03-20 23:42     ` John Stultz
2019-04-02  3:25 ` John Stultz

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