linux-kernel - Re: [PATCH V2] usb: gadget: f_fs: don't free buffer prematurely

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Date:   Wed, 24 Apr 2019 20:53:06 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     "Yang, Fei" <fei.yang@...el.com>, Felipe Balbi <balbi@...nel.org>,
        andrzej.p@...labora.com, Vincent Pelletier <plr.vincent@...il.com>,
        Linux USB List <linux-usb@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>, Josh Gao <jmgao@...gle.com>,
        Alistair Strachan <astrachan@...gle.com>,
        Shen Jing <jingx.shen@...el.com>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH V2] usb: gadget: f_fs: don't free buffer prematurely

On Wed, Apr 24, 2019 at 9:50 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Tue, Apr 02, 2019 at 10:26:51AM +0700, John Stultz wrote:
> > On Wed, Mar 20, 2019 at 11:21 AM John Stultz <john.stultz@...aro.org> wrote:
> > > On Wed, Mar 20, 2019 at 9:40 AM John Stultz <john.stultz@...aro.org> wrote:
> > > > On Tue, Mar 19, 2019 at 10:32 PM <fei.yang@...el.com> wrote:
> > > > 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.
> > >
> > > Felipe: Given Alan's point, does it make sense to mark the commits
> > > that remove the possible sleep from wait_event_lock_irq() in
> > > dwc3_gadget_ep_dequeue()  for -stable?
> > >
> > > Against 4.19.30, the following set manages to cherry-pick cleanly:
> > > git cherry-pick 1a22ec643580626f439c8583edafdcc73798f2fb
> > > git cherry-pick 09fe1f8d7e2f461275b1cdd832f2cfa5e9be346d
> > > git cherry-pick c3acd59014148470dc58519870fbc779785b4bf7
> > > git cherry-pick 7746a8dfb3f9c91b3a0b63a1d5c2664410e6498d
> > > git cherry-pick d5443bbf5fc8f8389cce146b1fc2987cdd229d12
> > > git cherry-pick d4f1afe5e896c18ae01099a85dab5e1a198bd2a8
> > > git cherry-pick fec9095bdef4e7c988adb603d0d4f92ee735d4a1
> > > # To get things building, revert modified -stable fix
> > > git revert 25ad17d
> > > #pick actual upstream fix replacing the previous
> > > git cherry-pick bd6742249b9ca918565e4e3abaa06665e587f4b5
> > >
> > > (Though I'm always a bit hesitant with -stable backports on subsystems
> > > I don't know well. So I'm not sure if this set is fully correct.)
> > >
> > > This set seems to avoid the crash on reboot I was seeing.
> > >
> > > And of course, I'm sure getting that set backported to 4.14 and 4.9
> > > (and maybe even 4.4, I need to check) will be less clean.
> >
> > Also,  I just wanted to follow up on this as well. Does the above set
> > of cherry-picks look ok to others for 4.19-stable?  Does anyone have
> > suggestions on how they'd like to see backports to 4.14, 4.9 and 4.4?
>
> If they are ok, can someone send me the commits as a series of patches,
> as doing the above really doesn't help much :)

Yea, so I'm happy to send that set to you for 4.19, assuming Felipe or
someone else OKs it.
I'm still at a bit of a loss for what to do for older (4.14/4.9/4.4)
-stable kernels, as its going to be difficult to backport those.

thanks
-john