[PATCH 6.8 074/143] rcu-tasks: Repair RCU Tasks Trace quiescence check

Greg Kroah-Hartman
2024-04-11T10:10:16Z

From: Paul E. McKenney <paulmck@kernel.org>

[ Upstream commit 2eb52fa8900e642b3b5054c4bf9776089d2a935f ]

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 <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 9d69e4bd6f0a8..17d7ed5f3ae6e 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