6.1-stable review patch. If anyone has any objections, please let me know.
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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 319698087d66a..6858cae98da9e 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -205,9 +205,9 @@ 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); \