rcu-tasks: Allow rcu_read_unlock_trace() under scheduler locks

The rcu_read_unlock_trace() can invoke rcu_read_unlock_trace_special(),
which in turn can call wake_up().  Therefore, if any scheduler lock is
held across a call to rcu_read_unlock_trace(), self-deadlock can occur.
This commit therefore uses the irq_work facility to defer the wake_up()
to a clean environment where no scheduler locks will be held.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
[ paulmck: Update #includes for m68k per kbuild test robot. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index a9e8ecb10860e797879d10f65c5c466e4c309194..dd311e93ed0ff0adbd5566a862dab932ba6a38e6 100644 (file)
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -729,6 +729,16 @@ void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
 DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace,
                 "RCU Tasks Trace");
 
+/*
+ * This irq_work handler allows rcu_read_unlock_trace() to be invoked
+ * while the scheduler locks are held.
+ */
+static void rcu_read_unlock_iw(struct irq_work *iwp)
+{
+       wake_up(&trc_wait);
+}
+static DEFINE_IRQ_WORK(rcu_tasks_trace_iw, rcu_read_unlock_iw);
+
 /* If we are the last reader, wake up the grace-period kthread. */
 void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
 {
@@ -742,7 +752,7 @@ void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
                WRITE_ONCE(t->trc_reader_special.b.need_qs, false);
        WRITE_ONCE(t->trc_reader_nesting, nesting);
        if (nq && atomic_dec_and_test(&trc_n_readers_need_end))
-               wake_up(&trc_wait);
+               irq_work_queue(&rcu_tasks_trace_iw);
 }
 EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special);
 

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index c5799349ff317ef25ee18ae55dd862fce54e01f1..b1f07a0e3a5697c64f96d67a71d739e053e7a650 100644 (file)
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -41,6 +41,7 @@
 #include <linux/sched/isolation.h>
 #include <linux/kprobes.h>
 #include <linux/slab.h>
+#include <linux/irq_work.h>
 
 #define CREATE_TRACE_POINTS