On Thu, Feb 25, 2016 at 09:11:44AM +0100, Peter Zijlstra wrote: > > Out of curiousity - where did that stray wakeup come from? PTRACE_KILL > > used to trigger those, but that got fixed. How does one trigger that > > kind of bugs on the current kernels? > > Its a regular TASK_INTERRUPTIBLE sleep, for those spurious wakeups are > not a bug, they're pretty fundamentally allowed.
They are, which makes any code that doesn't expect them in such situations buggy. > See: > lkml.kernel.org/r/CA+55aFwHkOo+YGWKYROmce1-H_uG3KfEUmCkJUerTj=ojy2...@mail.gmail.com I know. The question is not whether the code must take them into account (it must; it's a bug not to), it's what's a good way to trigger such bugs. IOW, how to stress-test for such bugs? PTRACE_KILL used to be a convenient way to arrange for a wakeup delivered to victim engaged in something we want to stress; it doesn't do blind wake_up_process() anymore, so that trick is gone. Is there anything similar? Suppose I have a dodgy waitqueue code (pardon the redundancy) in some filesystem. I have some idea how to maneuver a process into such-and-such part of that code; is there any convenient way to turn that into "... OK, now let's add bombing it with stray wakeups"?
