On Wed, Oct 7, 2020 at 9:29 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, Oct 07, 2020 at 07:30:51PM +0200, Andrey Konovalov wrote: > > Currently there's a KCOV remote coverage collection section in > > __usb_hcd_giveback_urb(). Initially that section was added based on the > > assumption that usb_hcd_giveback_urb() can only be called in interrupt > > context as indicated by a comment before it. > > > > As it turns out, it's actually valid to call usb_hcd_giveback_urb() in task > > context, provided that the caller turned off the interrupts; USB/IP actually > > does that. This can lead to a nested KCOV remote coverage collection > > sections both trying to collect coverage in task context. This isn't > > supported by KCOV, and leads to a WARNING. > > > > The approach this patch takes is to annotate every call of kcov_remote_*() > > callbacks with the context those callbacks are supposed to be executed in. > > If the current context doesn't match the mask provided to a callback, > > that callback is ignored. KCOV currently only supports collecting remote > > coverage in two contexts: task and softirq. > > > > As the result, the coverage from USB/IP related usb_hcd_giveback_urb() calls > > won't be collected, but the WARNING is fixed. > > > > A potential future improvement would be to support nested remote coverage > > collection sections, but this patch doesn't address that. > > > > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > > --- > > > --- a/drivers/usb/core/hcd.c > > +++ b/drivers/usb/core/hcd.c > > @@ -1646,9 +1646,9 @@ static void __usb_hcd_giveback_urb(struct urb *urb) > > > > /* pass ownership to the completion handler */ > > urb->status = status; > > - kcov_remote_start_usb((u64)urb->dev->bus->busnum); > > + kcov_remote_start_usb((u64)urb->dev->bus->busnum, KCOV_CONTEXT_SOFTIRQ); > > urb->complete(urb); > > - kcov_remote_stop(); > > + kcov_remote_stop(KCOV_CONTEXT_SOFTIRQ); > > This isn't right. __usb_hcd_giveback_urb() can execute in pretty much > any context; its constraint is that interrupts must be disabled. You're right, but here we constraint kcov to only collect coverage in case __usb_hcd_giveback_urb() is executed in softirq context. This is what happens when we're fuzzing USB with the dummy driver, which is the case we currently take care of. Whenever someone has a desire to collect coverage in other contexts, it will need to be implemented separately.
