rcu: Fix missing task information during rcu-preempt stall

The first item list_for_each_entry_continue(alist) iterates over is
alist->next, rather than alist itself. Consequently,
rcu_print_detail_task_stall_rnp() skips the task referenced by gp_tasks.

Use gp_tasks->prev as the argument to list_for_each_entry_continue()
instead.

Signed-off-by: Patrick Daly <pdaly@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index f8af20273868..853c7b8ea833 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -395,7 +395,7 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
                 return;
         }
-        t = list_entry(rnp->gp_tasks,
+        t = list_entry(rnp->gp_tasks->prev,
                        struct task_struct, rcu_node_entry);
         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
                 sched_show_task(t);
@@ -452,7 +452,7 @@ static int rcu_print_task_stall(struct rcu_node *rnp)
         if (!rcu_preempt_blocked_readers_cgp(rnp))
                 return 0;
         rcu_print_task_stall_begin(rnp);
-        t = list_entry(rnp->gp_tasks,
+        t = list_entry(rnp->gp_tasks->prev,
                        struct task_struct, rcu_node_entry);
         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
                 pr_cont(" P%d", t->pid);