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rcu: permit rcu_read_unlock() to be called while holding runqueue locks
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Avoid calling into the scheduler while holding core RCU locks.  This
allows rcu_read_unlock() to be called while holding the runqueue locks,
but only as long as there was no chance of the RCU read-side critical
section having been preempted.  (Otherwise, if RCU priority boosting
is enabled, rcu_read_unlock() might call into the scheduler in order to
unboost itself, which might allows self-deadlock on the runqueue locks
within the scheduler.)

Signed-off-by: Paul E. McKenney <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
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@paulmck
Paul E. McKenney authored and paulmck committed May 8, 2011
1 parent 29ce831 commit 1217ed1
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Showing 3 changed files with 34 additions and 79 deletions.
44 changes: 13 additions & 31 deletions kernel/rcutree.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1133,22 +1133,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (need_report & RCU_OFL_TASKS_EXP_GP)
rcu_report_exp_rnp(rsp, rnp);

/*
* If there are no more online CPUs for this rcu_node structure,
* kill the rcu_node structure's kthread. Otherwise, adjust its
* affinity.
*/
t = rnp->node_kthread_task;
if (t != NULL &&
rnp->qsmaskinit == 0) {
raw_spin_lock_irqsave(&rnp->lock, flags);
rnp->node_kthread_task = NULL;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
kthread_stop(t);
rcu_stop_boost_kthread(rnp);
} else
rcu_node_kthread_setaffinity(rnp, -1);
rcu_node_kthread_setaffinity(rnp, -1);
}

/*
Expand Down Expand Up @@ -1320,8 +1305,7 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
return;
}
if (rnp->qsmask == 0) {
rcu_initiate_boost(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
continue;
}
cpu = rnp->grplo;
Expand All @@ -1340,10 +1324,10 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
rnp = rcu_get_root(rsp);
raw_spin_lock_irqsave(&rnp->lock, flags);
if (rnp->qsmask == 0)
rcu_initiate_boost(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (rnp->qsmask == 0) {
raw_spin_lock_irqsave(&rnp->lock, flags);
rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
}
}

/*
Expand Down Expand Up @@ -1497,7 +1481,8 @@ static void invoke_rcu_cpu_kthread(void)

/*
* Wake up the specified per-rcu_node-structure kthread.
* The caller must hold ->lock.
* Because the per-rcu_node kthreads are immortal, we don't need
* to do anything to keep them alive.
*/
static void invoke_rcu_node_kthread(struct rcu_node *rnp)
{
Expand Down Expand Up @@ -1546,8 +1531,8 @@ static void rcu_cpu_kthread_timer(unsigned long arg)

raw_spin_lock_irqsave(&rnp->lock, flags);
rnp->wakemask |= rdp->grpmask;
invoke_rcu_node_kthread(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
invoke_rcu_node_kthread(rnp);
}

/*
Expand Down Expand Up @@ -1694,16 +1679,12 @@ static int rcu_node_kthread(void *arg)

for (;;) {
rnp->node_kthread_status = RCU_KTHREAD_WAITING;
wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0 ||
kthread_should_stop());
if (kthread_should_stop())
break;
wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0);
rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
raw_spin_lock_irqsave(&rnp->lock, flags);
mask = rnp->wakemask;
rnp->wakemask = 0;
rcu_initiate_boost(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
if ((mask & 0x1) == 0)
continue;
Expand All @@ -1719,6 +1700,7 @@ static int rcu_node_kthread(void *arg)
preempt_enable();
}
}
/* NOTREACHED */
rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
return 0;
}
Expand All @@ -1738,7 +1720,7 @@ static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
int cpu;
unsigned long mask = rnp->qsmaskinit;

if (rnp->node_kthread_task == NULL || mask == 0)
if (rnp->node_kthread_task == NULL)
return;
if (!alloc_cpumask_var(&cm, GFP_KERNEL))
return;
Expand Down
5 changes: 1 addition & 4 deletions kernel/rcutree.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -444,15 +444,12 @@ static void rcu_preempt_send_cbs_to_online(void);
static void __init __rcu_init_preempt(void);
static void rcu_needs_cpu_flush(void);
static void __init rcu_init_boost_waitqueue(struct rcu_node *rnp);
static void rcu_initiate_boost(struct rcu_node *rnp);
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
cpumask_var_t cm);
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
struct rcu_node *rnp,
int rnp_index);
#ifdef CONFIG_HOTPLUG_CPU
static void rcu_stop_boost_kthread(struct rcu_node *rnp);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

#endif /* #ifndef RCU_TREE_NONCORE */
64 changes: 20 additions & 44 deletions kernel/rcutree_plugin.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -711,15 +711,17 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
unsigned long flags;
int must_wait = 0;

raw_spin_lock(&rnp->lock); /* irqs already disabled */
if (!list_empty(&rnp->blkd_tasks)) {
raw_spin_lock_irqsave(&rnp->lock, flags);
if (list_empty(&rnp->blkd_tasks))
raw_spin_unlock_irqrestore(&rnp->lock, flags);
else {
rnp->exp_tasks = rnp->blkd_tasks.next;
rcu_initiate_boost(rnp);
rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
must_wait = 1;
}
raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
if (!must_wait)
rcu_report_exp_rnp(rsp, rnp);
}
Expand Down Expand Up @@ -1179,12 +1181,7 @@ static int rcu_boost(struct rcu_node *rnp)
*/
static void rcu_boost_kthread_timer(unsigned long arg)
{
unsigned long flags;
struct rcu_node *rnp = (struct rcu_node *)arg;

raw_spin_lock_irqsave(&rnp->lock, flags);
invoke_rcu_node_kthread(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
invoke_rcu_node_kthread((struct rcu_node *)arg);
}

/*
Expand All @@ -1200,10 +1197,7 @@ static int rcu_boost_kthread(void *arg)
for (;;) {
rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
wait_event_interruptible(rnp->boost_wq, rnp->boost_tasks ||
rnp->exp_tasks ||
kthread_should_stop());
if (kthread_should_stop())
break;
rnp->exp_tasks);
rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
more2boost = rcu_boost(rnp);
if (more2boost)
Expand All @@ -1215,7 +1209,7 @@ static int rcu_boost_kthread(void *arg)
spincnt = 0;
}
}
rnp->boost_kthread_status = RCU_KTHREAD_STOPPED;
/* NOTREACHED */
return 0;
}

Expand All @@ -1225,14 +1219,17 @@ static int rcu_boost_kthread(void *arg)
* kthread to start boosting them. If there is an expedited grace
* period in progress, it is always time to boost.
*
* The caller must hold rnp->lock.
* The caller must hold rnp->lock, which this function releases,
* but irqs remain disabled. The ->boost_kthread_task is immortal,
* so we don't need to worry about it going away.
*/
static void rcu_initiate_boost(struct rcu_node *rnp)
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
{
struct task_struct *t;

if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
rnp->n_balk_exp_gp_tasks++;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
if (rnp->exp_tasks != NULL ||
Expand All @@ -1242,11 +1239,14 @@ static void rcu_initiate_boost(struct rcu_node *rnp)
ULONG_CMP_GE(jiffies, rnp->boost_time))) {
if (rnp->exp_tasks == NULL)
rnp->boost_tasks = rnp->gp_tasks;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
t = rnp->boost_kthread_task;
if (t != NULL)
wake_up_process(t);
} else
} else {
rcu_initiate_boost_trace(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
}

/*
Expand Down Expand Up @@ -1312,27 +1312,11 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
return 0;
}

#ifdef CONFIG_HOTPLUG_CPU

static void rcu_stop_boost_kthread(struct rcu_node *rnp)
{
unsigned long flags;
struct task_struct *t;

raw_spin_lock_irqsave(&rnp->lock, flags);
t = rnp->boost_kthread_task;
rnp->boost_kthread_task = NULL;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (t != NULL)
kthread_stop(t);
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

#else /* #ifdef CONFIG_RCU_BOOST */

static void rcu_initiate_boost(struct rcu_node *rnp)
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
{
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}

static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
Expand All @@ -1355,14 +1339,6 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
return 0;
}

#ifdef CONFIG_HOTPLUG_CPU

static void rcu_stop_boost_kthread(struct rcu_node *rnp)
{
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

#endif /* #else #ifdef CONFIG_RCU_BOOST */

#ifndef CONFIG_SMP
Expand Down

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