If the caller of of call_rcu_tasks(), call_rcu_tasks_rude(),
or call_rcu_tasks_trace() holds a raw spinlock, and then if
call_rcu_tasks_generic() determines that the grace-period kthread must
be awakened, then the wakeup might acquire a normal spinlock while a
raw spinlock is held. This results in lockdep splats when the
kernel is built with CONFIG_PROVE_RAW_LOCK_NESTING=y.
This commit therefore defers the wakeup using irq_work_queue().
It would be nice to directly invoke wakeup when a raw spinlock is not
held, but there is currently no way to check for this in all kernels.
Reported-by: Martin Lau <kafai@xxxxxx>
Cc: Neeraj Upadhyay <neeraj.iitr10@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
kernel/rcu/tasks.h | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 3f25022a0db9a..652f51eec5f34 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -27,6 +27,7 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
* @rtp_jiffies: Jiffies counter value for statistics.
* @rtp_n_lock_retries: Rough lock-contention statistic.
* @rtp_work: Work queue for invoking callbacks.
+ * @rtp_irq_work: IRQ work queue for deferred wakeups.
* @barrier_q_head: RCU callback for barrier operation.
* @cpu: CPU number corresponding to this entry.
* @rtpp: Pointer to the rcu_tasks structure.
@@ -37,6 +38,7 @@ struct rcu_tasks_percpu {
unsigned long rtp_jiffies;
unsigned long rtp_n_lock_retries;
struct work_struct rtp_work;
+ struct irq_work rtp_irq_work;
struct rcu_head barrier_q_head;
int cpu;
struct rcu_tasks *rtpp;
@@ -102,9 +104,12 @@ struct rcu_tasks {
char *kname;
};
+static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp);
+
#define DEFINE_RCU_TASKS(rt_name, gp, call, n) \
static DEFINE_PER_CPU(struct rcu_tasks_percpu, rt_name ## __percpu) = { \
.lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name ## __percpu.cbs_pcpu_lock), \
+ .rtp_irq_work = IRQ_WORK_INIT(call_rcu_tasks_iw_wakeup), \
}; \
static struct rcu_tasks rt_name = \
{ \
@@ -230,6 +235,16 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
pr_info("%s: Setting shift to %d and lim to %d.\n", __func__, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim));
}
+// IRQ-work handler that does deferred wakeup for call_rcu_tasks_generic().
+static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
+{
+ struct rcu_tasks *rtp;
+ struct rcu_tasks_percpu *rtpcp = container_of(iwp, struct rcu_tasks_percpu, rtp_irq_work);
+
+ rtp = rtpcp->rtpp;
+ wake_up(&rtp->cbs_wq);
+}
+
// Enqueue a callback for the specified flavor of Tasks RCU.
static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
struct rcu_tasks *rtp)
@@ -262,8 +277,9 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
rcu_segcblist_enqueue(&rtpcp->cblist, rhp);
raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
/* We can't create the thread unless interrupts are enabled. */
- if (needwake && READ_ONCE(rtp->kthread_ptr))
- wake_up(&rtp->cbs_wq);
+ if (needwake && READ_ONCE(rtp->kthread_ptr)) {
+ irq_work_queue(&rtpcp->rtp_irq_work);
+ }
}
// Wait for a grace period for the specified flavor of Tasks RCU.
--
2.31.1.189.g2e36527f23
