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    SubjectRe: Is usb_hcd_giveback_urb() allowed in task context?
    On Mon, Oct 05, 2020 at 11:22:18AM -0400, Alan Stern 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.
    >
    > The primary reason for this restriction (as far as I'm aware) is because
    > the routine uses spin_lock/spin_unlock rather than the
    > _irqsave/_irqrestore variants. There's also a small efficiency issue:
    > In the vast majority of cases involving real host controllers, the
    > routine _will_ be called in interrupt context. So we optimized for that
    > case.
    >
    > > 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 USB/IP. Interrupts should be disabled when it calls
    > usb_hcd_giveback_urb().

    But that's not always the case when we have host controllers running
    with threaded interrupts, right? Or do they still disable interrupts?

    thanks,

    greg k-h

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