[PATCH tip/core/rcu 13/15] rcu: Make synchronize_sched_expedited() call wait_rcu_gp()

From: Paul E. McKenney
Date: Tue May 12 2015 - 17:46:10 EST

From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>

Currently, synchronize_sched_expedited() will call synchronize_sched()
if there is danger of counter wrap. But if configuration says to
always do expedited grace periods, synchronize_sched() will just
call synchronize_sched_expedited() right back again. In theory,
the old expedited operations will complete, the counters will
get back in synch, and the recursion will end. But we could
easily run out of stack long before that time. This commit
therefore makes synchronize_sched_expedited() invoke the underlying
wait_rcu_gp(call_rcu_sched) instead of synchronize_sched(), the same as
all the other calls out from synchronize_sched_expedited().

This bug was introduced by commit 1924bcb02597 (Avoid counter wrap in

Reported-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
kernel/rcu/tree.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 5b573e75e0f8..647dee075d99 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3288,7 +3288,7 @@ void synchronize_sched_expedited(void)
if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start),
(ulong)atomic_long_read(&rsp->expedited_done) +
ULONG_MAX / 8)) {
- synchronize_sched();
+ wait_rcu_gp(call_rcu_sched);

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/