On Wed, Jun 24, 2015 at 10:42:48AM +0200, Ingo Molnar wrote: > > * Peter Zijlstra <pet...@infradead.org> wrote: > > > On Tue, Jun 23, 2015 at 11:26:26AM -0700, Paul E. McKenney wrote: > > > > > > > > I really think you're making that expedited nonsense far too accessible. > > > > > > This has nothing to do with accessibility and everything to do with > > > robustness. And with me not becoming the triage center for too many > > > non-RCU > > > bugs. > > > > But by making it so you're rewarding abuse instead of flagging it :-( > > Btw., being a 'triage center' is the bane of APIs that are overly successful, > so we should take that burden with pride! :-)
I will gladly accept that compliment. And the burden. But, lazy as I am, I intend to automate it. ;-) > Lockdep (and the scheduler APIs as well) frequently got into such situations > as > well, and we mostly solved it by being more informative with debug splats. > > I don't think a kernel API should (ever!) stay artificially silent, just for > fear > of flagging too many problems in other code. I agree, as attested by RCU CPU stall warnings, lockdep-RCU, sparse-based RCU checks, and the object-debug-based checks for double call_rcu(). That said, in all of these cases, including your example of lockdep, the diagnostic is a debug splat rather than a mutex-contention meltdown. And it is the mutex-contention meltdown that I will continue making synchronize_sched_expedited() avoid. But given the change from bulk try_stop_cpus() to either stop_one_cpu() or IPIs, it would not be hard to splat if a given CPU didn't come back fast enough. The latency tracer would of course provide better information, but synchronize_sched_expedited() could do a coarse-grained job with less setup required. My first guess for the timeout would be something like 500 milliseconds. Thoughts? Thanx, Paul -- 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/