On Thu, Aug 07, 2014 at 03:49:07PM -0400, Steven Rostedt wrote: > On Thu, 7 Aug 2014 20:46:35 +0200 > Peter Zijlstra <pet...@infradead.org> wrote: > > > On Thu, Aug 07, 2014 at 07:27:53PM +0200, Peter Zijlstra wrote: > > > Right, Steve (and Paul) please explain _why_ this is an 'RCU' at all? > > > _Why_ do we have call_rcu_task(), and why is it entwined in the 'normal' > > > RCU stuff? We've got SRCU -- which btw started out simple, without > > > call_srcu() -- and that lives entirely independent. And SRCU is far more > > > an actual RCU than this thing is, its got read side primitives and > > > everything. > > > > > > Also, I cannot think of any other use besides trampolines for this > > > thing, but that might be my limited imagination. > > > > Also, trampolines can end up in the return frames, right? So how can you > > be sure when to wipe them? Passing through schedule() isn't enough for > > that. > > Not sure what you mean.
void bar() { mutex_lock(); ... mutex_unlock(); } void foo() { bar(); } Normally that'll give you a stack/return frame like: foo() bar() mutex_lock() schedule(); Now suppose there's a trampoline around bar(), that would give: foo() __trampoline() bar() mutex_lock() schedule() so the function return of bar doesn't point to foo, but to the trampoline. But we call schedule() from mutex_lock() and think we're all good. > > Userspace is, but kernel threads typically don't ever end up there. > Hence, once something calls schedule() directly, we know that it is not > on a trampoline, nor is it going to return to one. How can you say its not going to return to one? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/