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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>
This commit is contained in:
Paul E. McKenney 2016-05-02 11:58:56 -07:00
parent 570dd3c742
commit 4929c913bd
2 changed files with 6 additions and 2 deletions
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1
include/linux/rcupdate.h
View File

@ -45,6 +45,7 @@
#include <linux/bug.h>
#include <linux/compiler.h>
#include <linux/ktime.h>
#include <linux/irqflags.h>
#include <asm/barrier.h>

7
kernel/rcu/update.c
View File

@ -528,6 +528,7 @@ static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10;
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 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
{
unsigned long flags;
bool needwake;
bool havetask = READ_ONCE(rcu_tasks_kthread_ptr);
rhp->next = NULL;
rhp->func = func;
@ -545,7 +547,9 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
*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 int __noreturn rcu_tasks_kthread(void *arg)
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)) {