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Commit 4929c913 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 570dd3c7

include/linux/rcupdate.h

+1 −0
Original line number Diff line number Diff line
@@ -45,6 +45,7 @@ 
#include <linux/bug.h>

#include <linux/compiler.h>

#include <linux/ktime.h>

#include <linux/irqflags.h>



#include <asm/barrier.h>

kernel/rcu/update.c

+5 −2
Original line number Diff line number Diff line
@@ -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)) {