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

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Date:   Tue, 2 Apr 2019 10:26:51 +0700
From:   John Stultz <john.stultz@...aro.org>
To:     "Yang, Fei" <fei.yang@...el.com>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg KH <gregkh@...uxfoundation.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, 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?

thanks
-john