Commit-ID: 2f51f9884f6a36b0fe9636d5a1937e5cbd25723b
Gitweb: http://git.kernel.org/tip/2f51f9884f6a36b0fe9636d5a1937e5cbd25723b
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Fri, 13 Nov 2009 19:51:39 -0800
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Sat, 14 Nov 2009 10:31:42 +0100
rcu: Eliminate __rcu_pending() false positives
Now that there are both ->gpnum and ->completed fields in the
rcu_node structure, __rcu_pending() should check rdp->gpnum and
rdp->completed against rnp->gpnum and rdp->completed, respectively,
instead of the prior comparison against the rcu_state fields
rsp->gpnum and rsp->completed.
Given the old comparison, __rcu_pending() could return 1, resulting
in a needless raise_softirq(RCU_SOFTIRQ). This useless work would
happen if RCU responded to a scheduling-clock interrupt after the
rcu_state fields had been updated, but before the rcu_node fields
had been updated.
Changing the comparison from the rcu_state fields to the rcu_node
fields prevents this useless work from happening.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: laijs@xxxxxxxxxxxxxx
Cc: dipankar@xxxxxxxxxx
Cc: mathieu.desnoyers@xxxxxxxxxx
Cc: josh@xxxxxxxxxxxxxxxx
Cc: dvhltc@xxxxxxxxxx
Cc: niv@xxxxxxxxxx
Cc: peterz@xxxxxxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
Cc: Valdis.Kletnieks@xxxxxx
Cc: dhowells@xxxxxxxxxx
LKML-Reference: <12581706991966-git-send-email->
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
kernel/rcutree.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 24bbf2c..9b36d6d 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1403,6 +1403,8 @@ EXPORT_SYMBOL_GPL(call_rcu_bh);
*/
static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
{
+ struct rcu_node *rnp = rdp->mynode;
+
rdp->n_rcu_pending++;
/* Check for CPU stalls, if enabled. */
@@ -1427,13 +1429,13 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
}
/* Has another RCU grace period completed? */
- if (ACCESS_ONCE(rsp->completed) != rdp->completed) { /* outside lock */
+ if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
rdp->n_rp_gp_completed++;
return 1;
}
/* Has a new RCU grace period started? */
- if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) { /* outside lock */
+ if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
rdp->n_rp_gp_started++;
return 1;
}
--
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