kcov: simplify interrupt check

in_interrupt() semantics are confusing and wrong for most users as it
also returns true when bh is disabled.  Thus we open coded a proper
check for interrupts in __sanitizer_cov_trace_pc() with a lengthy
explanatory comment.

Use the new in_task() predicate instead.

Link: http://lkml.kernel.org/r/20170321091026.139655-1-dvyukov@google.com


Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: James Morse <james.morse@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>