From: "Paul E. McKenney" <paul...@kernel.org>
The context-switch-time check for RCU Tasks Trace quiescence expects
current->trc_reader_special.b.need_qs to be zero, and if so, updates
it to TRC_NEED_QS_CHECKED. This is backwards, because if this value
is zero, there is no RCU Tasks Trace grace period in flight, an thus
no need for a quiescent state. Instead, when a grace period starts,
this field is set to TRC_NEED_QS.
This commit therefore changes the check from zero to TRC_NEED_QS.
Reported-by: Steven Rostedt <rost...@goodmis.org>
Signed-off-by: Paul E. McKenney <paul...@kernel.org>
Tested-by: Steven Rostedt (Google) <rost...@goodmis.org>
Signed-off-by: Boqun Feng <boqun.f...@gmail.com>
---
include/linux/rcupdate.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 0746b1b0b663..16f519914415 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -184,9 +184,9 @@ void rcu_tasks_trace_qs_blkd(struct task_struct *t);
do {
\
int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting);
\
\
- if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) &&
\
+ if (unlikely(READ_ONCE((t)->trc_reader_special.b.need_qs) ==
TRC_NEED_QS) && \
likely(!___rttq_nesting)) {
\
- rcu_trc_cmpxchg_need_qs((t), 0, TRC_NEED_QS_CHECKED);
\
+ rcu_trc_cmpxchg_need_qs((t), TRC_NEED_QS,
TRC_NEED_QS_CHECKED); \
} else if (___rttq_nesting && ___rttq_nesting != INT_MIN &&
\
!READ_ONCE((t)->trc_reader_special.b.blocked)) {
\
rcu_tasks_trace_qs_blkd(t);
\
--
2.43.0
