linux-kernel - Re: Is usb_hcd_giveback_urb() allowed in task context?

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Message-ID: <CAAeHK+zes2Y00+EJ6SVtOHj8YCADw5WSXUEFHWCRgxi=H42+4w@mail.gmail.com>
Date:   Mon, 5 Oct 2020 17:21:30 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Valentina Manea <valentina.manea.m@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Nazime Hande Harputluoglu <handeharputlu@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: Is usb_hcd_giveback_urb() allowed in task context?

On Mon, Oct 5, 2020 at 5:18 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Mon, Oct 05, 2020 at 05:08:11PM +0200, Andrey Konovalov wrote:
> > Dear USB and USB/IP maintainers,
> >
> > While fuzzing the USB/IP stack with syzkaller we've stumbled upon an issue.
> >
> > Currently kcov (the subsystem that is used for coverage collection)
> > USB-related callbacks assume that usb_hcd_giveback_urb() can only be
> > called from interrupt context, as indicated by the comment before the
> > function definition. In the USB/IP code, however, it's called from the
> > task context (see the stack trace below).
> >
> > Is this something that is allowed and we need to fix kcov? Or is this
> > a bug in USB/IP?
>
> It's a bug in kcov, and is not true as you have found out :)

OK, I see, I'll work on a fix, thanks!

Should I also update the comment above usb_hcd_giveback_urb() to
mention that it can be called in_task()? Or is this redundant and is
assumed in general?