On Wed, Oct 7, 2020 at 10:07 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, Oct 07, 2020 at 09:54:57PM +0200, Andrey Konovalov wrote: > > 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. > > Oh, sorry. I thought the constraint meant that it would be an error > if kcov observed __usb_hcd_giveback_urb() executing in anything other > than softirq context. Ah, no, it will just be ignored. But I'll clarify this in v2, thank you!
