Messages in this thread Patch in this message | | | Date | Tue, 12 Aug 2014 14:39:36 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 1/2] rcu: Parallelize and economize NOCB kthread wakeups |
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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.
Thanx, Paul
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diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index a2333d07f5d6..1dc72f523c4a 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2043,7 +2043,7 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force) if (!ACCESS_ONCE(rdp_leader->nocb_kthread)) return; if (!ACCESS_ONCE(rdp_leader->nocb_leader_wake) || force) { - /* Prior xchg orders against prior callback enqueue. */ + /* Prior smp_mb__after_atomic() orders against prior enqueue. */ ACCESS_ONCE(rdp_leader->nocb_leader_wake) = true; wake_up(&rdp_leader->nocb_wq); } @@ -2072,6 +2072,7 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, ACCESS_ONCE(*old_rhpp) = rhp; atomic_long_add(rhcount, &rdp->nocb_q_count); atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); + smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */ /* If we are not being polled and there is a kthread, awaken it ... */ t = ACCESS_ONCE(rdp->nocb_kthread);
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