Messages in this thread Patch in this message | | | Date | Tue, 12 Aug 2014 14:41:51 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 1/2] rcu: Parallelize and economize NOCB kthread wakeups |
| |
On Tue, Aug 12, 2014 at 02:39:36PM -0700, Paul E. McKenney wrote: > On Tue, Aug 12, 2014 at 09:06:21AM -0700, Paul E. McKenney wrote: > > On Tue, Aug 12, 2014 at 11:03:21AM +0530, Amit Shah wrote: > > [ . . . ] > > > > I know of only virtio-console doing this (via userspace only, > > > though). > > > > As in userspace within the guest? That would not work. The userspace > > that the qemu is running in might. There is a way to extract ftrace info > > from crash dumps, so one approach would be "sendkey alt-sysrq-c", then > > pull the buffer from the resulting dump. For all I know, there might also > > be some script that uses the qemu "x" command to get at the ftrace buffer. > > > > Again, I cannot reproduce this, and I have been through the code several > > times over the past few days, and am not seeing it. I could start > > sending you random diagnostic patches, but it would be much better if > > we could get the trace data from the failure. > > Hearing no objections, random patch #1. The compiler could in theory > cause trouble without this patch, so there is some possibility that > it is a fix.
#2... This would have been a problem without the earlier patch, but who knows? (#1 moved from theoretically possible but not on x86 to maybe on x86 given a sufficiently malevolent compiler with the patch that you located with bisection.)
Thanx, Paul
------------------------------------------------------------------------
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 1dc72f523c4a..1da605740e8d 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2137,6 +2137,17 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, trace_rcu_callback(rdp->rsp->name, rhp, -atomic_long_read(&rdp->nocb_q_count_lazy), -atomic_long_read(&rdp->nocb_q_count)); + + /* + * If called from an extended quiescent state with interrupts + * disabled, invoke the RCU core in order to allow the idle-entry + * deferred-wakeup check to function. + */ + if (irqs_disabled_flags(flags) && + !rcu_is_watching() && + cpu_online(smp_processor_id())) + invoke_rcu_core(); + return true; }
| |