queue-6.1/rcu-tasks-repair-rcu-tasks-trace-quiescence-check.patch

   1 From 5aca326b8ef12decce747927124008e1de957c4a Mon Sep 17 00:00:00 2001
   2 From: Sasha Levin <sashal@kernel.org>
   3 Date: Mon, 4 Dec 2023 09:33:29 -0800
   4 Subject: rcu-tasks: Repair RCU Tasks Trace quiescence check
   5
   6 From: Paul E. McKenney <paulmck@kernel.org>
   7
   8 [ Upstream commit 2eb52fa8900e642b3b5054c4bf9776089d2a935f ]
   9
  10 The context-switch-time check for RCU Tasks Trace quiescence expects
  11 current->trc_reader_special.b.need_qs to be zero, and if so, updates
  12 it to TRC_NEED_QS_CHECKED.  This is backwards, because if this value
  13 is zero, there is no RCU Tasks Trace grace period in flight, an thus
  14 no need for a quiescent state.  Instead, when a grace period starts,
  15 this field is set to TRC_NEED_QS.
  16
  17 This commit therefore changes the check from zero to TRC_NEED_QS.
  18
  19 Reported-by: Steven Rostedt <rostedt@goodmis.org>
  20 Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
  21 Tested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
  22 Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
  23 Signed-off-by: Sasha Levin <sashal@kernel.org>
  24 ---
  25  include/linux/rcupdate.h | 4 ++--
  26  1 file changed, 2 insertions(+), 2 deletions(-)
  27
  28 diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
  29 index 319698087d66a..6858cae98da9e 100644
  30 --- a/include/linux/rcupdate.h
  31 +++ b/include/linux/rcupdate.h
  32 @@ -205,9 +205,9 @@ void rcu_tasks_trace_qs_blkd(struct task_struct *t);
  33         do {                                                                    \
  34                 int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting);       \
  35                                                                                 \
  36 -               if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) &&    \
  37 +               if (unlikely(READ_ONCE((t)->trc_reader_special.b.need_qs) == TRC_NEED_QS) &&    \
  38                     likely(!___rttq_nesting)) {                                 \
  39 -                       rcu_trc_cmpxchg_need_qs((t), 0, TRC_NEED_QS_CHECKED);   \
  40 +                       rcu_trc_cmpxchg_need_qs((t), TRC_NEED_QS, TRC_NEED_QS_CHECKED); \
  41                 } else if (___rttq_nesting && ___rttq_nesting != INT_MIN &&     \
  42                            !READ_ONCE((t)->trc_reader_special.b.blocked)) {     \
  43                         rcu_tasks_trace_qs_blkd(t);                             \
  44 --
  45 2.43.0
  46