When force_qs_rnp() forces quiescent states for idle or offline CPUs, any tasks blocked on those CPUs' per-CPU blocked lists must first be promoted to the rcu_node's blkd_tasks list.
Without this promotion, blocked tasks on per-CPU lists won't have gp_tasks point to them, so the GP machinery won't wait for them. This can cause "Wrong-GP reads" errors where a GP completes while readers are still in their critical sections. Therefore, call rcu_promote_blocked_tasks_rdp() before reporting QS. Signed-off-by: Joel Fernandes <[email protected]> --- kernel/rcu/tree.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 2a20b1a8c5d3..19fd13c1e6be 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2790,6 +2790,11 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) rdp = per_cpu_ptr(&rcu_data, cpu); ret = f(rdp); if (ret > 0) { + /* + * Promote blocked tasks before reporting QS. + * Otherwise tasks on per-CPU list aren't tracked. + */ + rcu_promote_blocked_tasks_rdp(rdp, rnp); mask |= rdp->grpmask; rcu_disable_urgency_upon_qs(rdp); } -- 2.34.1
