Commit 2eb52fa8 authored Dec 04, 2023 by Paul E. McKenney Committed by Boqun Feng Feb 14, 2024

rcu-tasks: Repair RCU Tasks Trace quiescence check



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>

parent 41bccc98

include/linux/rcupdate.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -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); \