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 <andreyk...@google.com> > ---
> --- 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. Alan Stern
