On Mon, Mar 28, 2011 at 06:46:48PM +0200, Sedat Dilek wrote:
> On Mon, Mar 28, 2011 at 6:38 PM, Sedat Dilek <sedat.dilek@xxxxxxxxxxxxxx> wrote:
> > On Mon, Mar 28, 2011 at 5:11 PM, Paul E. McKenney
> > <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> >> On Mon, Mar 28, 2011 at 06:24:36AM -0700, Paul E. McKenney wrote:
> >>> On Mon, Mar 28, 2011 at 02:33:36PM +0200, Sedat Dilek wrote:
[ . . . ]
> >>> > Ah, before I forget...
> >>> >
> >>> > I used TREE_RCU (was the default before noticing RCU issue) for
> >>> > finding the culprit commit.
> >>> > If it is from your POV more helpful to switch to PREEMPT + PREEMPT_RCU
> >>> > + RCU_BOOST, please let me *now* know.
> >>> > ( Both RCU setups freaks up the system. )
> >>>
> >>> If TREE_RCU hits problems faster, it is probably best to stay with
> >>> TREE_RCU.
> >>
> >> And of course, one exception to this advice is if TREE_RCU hangs so hard
> >> and fast that you don't have time to get any diagnostics. If this is the
> >> case, then TREE_PREEMPT_RCU might be more productive.
> >>
> >
> > OK, that would somehow explain why I could not really get some debug
> > infos when doing "my stress-test" and checking via:
> >
> > $ LC_ALL=C tail -f /sys/kernel/debug/rcu/rcudata
> >
> > Then I remembered I saw a snippet for a RCU torture script mentionned
> > in the kernel-docs (see Documentation/RCU/torture.txt).
> >
> > 189 The following script may be used to torture RCU:
> > 190
> > 191 #!/bin/sh
> > 192
> > 193 modprobe rcutorture
> > 194 sleep 100
> > 195 rmmod rcutorture
> > 196 dmesg | grep torture:
> >
> > So, I recompiled a new TREE_RC-based kernel and build with
> > CONFIG_RCU_TORTURE_TEST=m.
> >
> > Unfortunately, the rmmod (I prefer modprobe -r -v) hangs... the
> > messages in the logs look promising.
> >
> > - Sedat -
> >
>
> Wrong attachment, correct attached.
And one stupid problem located thus far. I can make a (tortured) case
for it resulting in the symptoms you see, but it does seem unlikely to
happen repeatedly, as it would require a burst of CPU just at the wrong
time. But who knows?
In any case, I am still looking.
Thanx, Paul
------------------------------------------------------------------------
Fix stupid typo.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 5477764..f311228 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1618,7 +1618,7 @@ static int rcu_node_kthread(void *arg)
rnp->wakemask = 0;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
rcu_initiate_boost(rnp);
- for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
if ((mask & 0x1) == 0)
continue;
preempt_disable();
--
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