On 6/16/15 9:05 AM, Paul E. McKenney wrote:
On Tue, Jun 16, 2015 at 11:37:38AM -0400, Steven Rostedt wrote:
On Tue, 16 Jun 2015 05:27:33 -0700
"Paul E. McKenney" <[email protected]> wrote:
On Mon, Jun 15, 2015 at 10:45:05PM -0700, Alexei Starovoitov wrote:
On 6/15/15 7:14 PM, Paul E. McKenney wrote:
Why do you believe that it is better to fix it within call_rcu()?
found it:
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8cf7304b2867..a3be09d482ae 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -935,9 +935,9 @@ bool notrace rcu_is_watching(void)
{
bool ret;
- preempt_disable();
+ preempt_disable_notrace();
ret = __rcu_is_watching();
- preempt_enable();
+ preempt_enable_notrace();
return ret;
}
the rcu_is_watching() and __rcu_is_watching() are already marked
notrace, so imo it's a good 'fix'.
What was happening is that the above preempt_enable was triggering
recursive call_rcu that was indeed messing 'rdp' that was
prepared by __call_rcu and before __call_rcu_core could use that.
btw, also noticed that local_irq_save done by note_gp_changes
is partially redundant. In __call_rcu_core path the irqs are
already disabled.
If rcu_is_watching() and __rcu_is_watching() are both marked as
notrace, it makes sense to use preempt_disable/enable_notrace() as it
otherwise defeats the purpose of the notrace markers on rcu_is_watching.
That is regardless of what the rest of this thread is about.
Good enough! Alexei, are you OK with my adding your Signed-off-by
to the above patch?
sure.
Signed-off-by: Alexei Starovoitov <[email protected]>
(Still not sold on reentrant call_rcu() and
kfree_rcu(), but getting notrace set up correctly is worthwhile.)
I'm not sold on it either. So far trying to understand
all consequences.
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