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Code Issues Releases Wiki Activity

rcu-tasks: Make rcu_barrier_tasks*() handle multiple callback queues

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Currently, rcu_barrier_tasks(), rcu_barrier_tasks_rude(),
and rcu_barrier_tasks_trace() simply invoke the corresponding
synchronize_rcu_tasks*() function.  This works because there is only
one callback queue.

However, there will soon be multiple callback queues.  This commit
therefore scans the queues currently in use, entraining a callback on
each non-empty queue.  Sequence numbers and reference counts are used
to synchronize this process in a manner similar to the approach taken
by rcu_barrier().

Reported-by: Martin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-11-11 14:53:43 -08:00
parent d363f833c6
commit ce9b1c667f
1 changed files with 64 additions and 6 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

70
kernel/rcu/tasks.h
View file

@ -25,11 +25,15 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
* @cblist: Callback list.
* @lock: Lock protecting per-CPU callback list.
* @rtp_work: Work queue for invoking callbacks.
* @barrier_q_head: RCU callback for barrier operation.
* @cpu: CPU number corresponding to this entry.
* @rtpp: Pointer to the rcu_tasks structure.
*/
struct rcu_tasks_percpu {
struct rcu_segcblist cblist;
raw_spinlock_t __private lock;
struct work_struct rtp_work;
struct rcu_head barrier_q_head;
int cpu;
struct rcu_tasks *rtpp;
};
@ -57,6 +61,10 @@ struct rcu_tasks_percpu {
* @rtpcpu: This flavor's rcu_tasks_percpu structure.
* @percpu_enqueue_shift: Shift down CPU ID this much when enqueuing callbacks.
* @percpu_enqueue_lim: Number of per-CPU callback queues in use.
* @barrier_q_mutex: Serialize barrier operations.
* @barrier_q_count: Number of queues being waited on.
* @barrier_q_completion: Barrier wait/wakeup mechanism.
* @barrier_q_seq: Sequence number for barrier operations.
* @name: This flavor's textual name.
* @kname: This flavor's kthread name.
*/
@ -82,6 +90,10 @@ struct rcu_tasks {
struct rcu_tasks_percpu __percpu *rtpcpu;
int percpu_enqueue_shift;
int percpu_enqueue_lim;
struct mutex barrier_q_mutex;
atomic_t barrier_q_count;
struct completion barrier_q_completion;
unsigned long barrier_q_seq;
char *name;
char *kname;
};
@ -100,6 +112,8 @@ static struct rcu_tasks rt_name = \
.name = n, \
.percpu_enqueue_shift = ilog2(CONFIG_NR_CPUS), \
.percpu_enqueue_lim = 1, \
.barrier_q_mutex = __MUTEX_INITIALIZER(rt_name.barrier_q_mutex), \
.barrier_q_seq = (0UL - 50UL) << RCU_SEQ_CTR_SHIFT, \
.kname = #rt_name, \
}
@ -238,6 +252,53 @@ static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp)
wait_rcu_gp(rtp->call_func);
}
// RCU callback function for rcu_barrier_tasks_generic().
static void rcu_barrier_tasks_generic_cb(struct rcu_head *rhp)
{
struct rcu_tasks *rtp;
struct rcu_tasks_percpu *rtpcp;
rtpcp = container_of(rhp, struct rcu_tasks_percpu, barrier_q_head);
rtp = rtpcp->rtpp;
if (atomic_dec_and_test(&rtp->barrier_q_count))
complete(&rtp->barrier_q_completion);
}
// Wait for all in-flight callbacks for the specified RCU Tasks flavor.
// Operates in a manner similar to rcu_barrier().
static void rcu_barrier_tasks_generic(struct rcu_tasks *rtp)
{
int cpu;
unsigned long flags;
struct rcu_tasks_percpu *rtpcp;
unsigned long s = rcu_seq_snap(&rtp->barrier_q_seq);
mutex_lock(&rtp->barrier_q_mutex);
if (rcu_seq_done(&rtp->barrier_q_seq, s)) {
smp_mb();
mutex_unlock(&rtp->barrier_q_mutex);
return;
}
rcu_seq_start(&rtp->barrier_q_seq);
init_completion(&rtp->barrier_q_completion);
atomic_set(&rtp->barrier_q_count, 2);
for_each_possible_cpu(cpu) {
if (cpu >= smp_load_acquire(&rtp->percpu_enqueue_lim))
break;
rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
rtpcp->barrier_q_head.func = rcu_barrier_tasks_generic_cb;
raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
if (rcu_segcblist_entrain(&rtpcp->cblist, &rtpcp->barrier_q_head))
atomic_inc(&rtp->barrier_q_count);
raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
}
if (atomic_sub_and_test(2, &rtp->barrier_q_count))
complete(&rtp->barrier_q_completion);
wait_for_completion(&rtp->barrier_q_completion);
rcu_seq_end(&rtp->barrier_q_seq);
mutex_unlock(&rtp->barrier_q_mutex);
}
// Advance callbacks and indicate whether either a grace period or
// callback invocation is needed.
static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
@ -703,8 +764,7 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
*/
void rcu_barrier_tasks(void)
{
/* There is only one callback queue, so this is easy. ;-) */
synchronize_rcu_tasks();
rcu_barrier_tasks_generic(&rcu_tasks);
}
EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
@ -842,8 +902,7 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_rude);
*/
void rcu_barrier_tasks_rude(void)
{
/* There is only one callback queue, so this is easy. ;-) */
synchronize_rcu_tasks_rude();
rcu_barrier_tasks_generic(&rcu_tasks_rude);
}
EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude);
@ -1401,8 +1460,7 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_trace);
*/
void rcu_barrier_tasks_trace(void)
{
/* There is only one callback queue, so this is easy. ;-) */
synchronize_rcu_tasks_trace();
rcu_barrier_tasks_generic(&rcu_tasks_trace);
}
EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace);