rcu: Make call_rcu_tasks() tolerate first call with irqs disabled
Currently, if the very first call to call_rcu_tasks() has irqs disabled,
it will create the rcu_tasks_kthread with irqs disabled, which will
result in a splat in the memory allocator, which kthread_run() invokes
with the expectation that irqs are enabled.
This commit fixes this problem by deferring kthread creation if called
with irqs disabled. The first call to call_rcu_tasks() that has irqs
enabled will create the kthread.
This bug was detected by rcutorture changes that were motivated by
Iftekhar Ahmed's mutation-testing efforts.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index a8af797..3bc5de0 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -45,6 +45,7 @@
#include <linux/bug.h>
#include <linux/compiler.h>
#include <linux/ktime.h>
+#include <linux/irqflags.h>
#include <asm/barrier.h>
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 3e888cd..f0d8322 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -528,6 +528,7 @@
module_param(rcu_task_stall_timeout, int, 0644);
static void rcu_spawn_tasks_kthread(void);
+static struct task_struct *rcu_tasks_kthread_ptr;
/*
* Post an RCU-tasks callback. First call must be from process context
@@ -537,6 +538,7 @@
{
unsigned long flags;
bool needwake;
+ bool havetask = READ_ONCE(rcu_tasks_kthread_ptr);
rhp->next = NULL;
rhp->func = func;
@@ -545,7 +547,9 @@
*rcu_tasks_cbs_tail = rhp;
rcu_tasks_cbs_tail = &rhp->next;
raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
- if (needwake) {
+ /* We can't create the thread unless interrupts are enabled. */
+ if ((needwake && havetask) ||
+ (!havetask && !irqs_disabled_flags(flags))) {
rcu_spawn_tasks_kthread();
wake_up(&rcu_tasks_cbs_wq);
}
@@ -790,7 +794,6 @@
static void rcu_spawn_tasks_kthread(void)
{
static DEFINE_MUTEX(rcu_tasks_kthread_mutex);
- static struct task_struct *rcu_tasks_kthread_ptr;
struct task_struct *t;
if (READ_ONCE(rcu_tasks_kthread_ptr)) {