On Tue, Nov 24, 2020 at 12:47:25AM +0100, 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. This is what happens when > syzkaller is fuzzing the USB stack via the dummy_hcd driver. > > 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 does > exactly 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. > > Change __usb_hcd_giveback_urb() to only call kcov_remote_*() callbacks > when it's being executed in a softirq. To avoid calling > in_serving_softirq() directly in the driver code, add a couple of new kcov > wrappers. > > As the result of this change, 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> > Acked-by: Marco Elver <elver@xxxxxxxxxx> > --- > > Changes in v5: > - Don't call in_serving_softirq() in USB driver code directly, do that > via kcov wrappers. Does not apply to 5.11-rc1 :(
