kcov, usb: Don't disable interrupts in kcov_remote_start_usb_softirq()

kcov, usb: Don't disable interrupts in kcov_remote_start_usb_softirq()

kcov_remote_start_usb_softirq() the begin of urb's completion callback.
HCDs marked HCD_BH will invoke this function from the softirq and
in_serving_softirq() will detect this properly.
Root-HUB (RH) requests will not be delayed to softirq but complete
immediately in IRQ context.
This will confuse kcov because in_serving_softirq() will report true if
the softirq is served after the hardirq and if the softirq got
interrupted by the hardirq in which currently runs.

This was addressed by simply disabling interrupts in
kcov_remote_start_usb_softirq() which avoided the interruption by the RH
while a regular completion callback was invoked.
This not only changes the behaviour while kconv is enabled but also
breaks PREEMPT_RT because now sleeping locks can no longer be acquired.

Revert the previous fix. Address the issue by invoking
kcov_remote_start_usb() only if the context is just "serving softirqs"
which is identified by checking in_serving_softirq() and in_hardirq()
must be false.

Fixes: f85d39dd7ed89 ("kcov, usb: disable interrupts in kcov_remote_start_usb_softirq")
Cc: stable <stable@kernel.org>
Reported-by: Yunseong Kim <ysk@kzalloc.com>
Closes: https://lore.kernel.org/all/20250725201400.1078395-2-ysk@kzalloc.com/
Tested-by: Yunseong Kim <ysk@kzalloc.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20250811082745.ycJqBXMs@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>