[PATCH v2 4/4] perf: Split __perf_pending_irq() out of perf_pending_irq()

Sebastian Andrzej Siewior
2024-03-12T18:08:22Z

perf_pending_irq() invokes perf_event_wakeup() and __perf_pending_irq().
The former is in charge of waking any tasks which wait to be woken up
while the latter disables perf-events.

The irq_work perf_pending_irq(), while this an irq_work, the callback
is invoked in thread context on PREEMPT_RT. This is needed because all
the waking functions (wake_up_all(), kill_fasync()) acquire sleep locks
which must not be used with disabled interrupts.
Disabling events, as done by __perf_pending_irq(), expects a hardirq
context and disabled interrupts. This requirement is not fulfilled on
PREEMPT_RT.

Split functionality based on perf_event::pending_disable into irq_work
named `pending_disable_irq' and invoke it in hardirq context on
PREEMPT_RT. Rename the split out callback to perf_pending_disable().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/perf_event.h | 1 +
kernel/events/core.c | 31 +++++++++++++++++++++++--------
2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 24ac6765146c7..c1c6600541657 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -783,6 +783,7 @@ struct perf_event {
unsigned int pending_disable;
unsigned long pending_addr; /* SIGTRAP */
struct irq_work pending_irq;
+ struct irq_work pending_disable_irq;
struct callback_head pending_task;
unsigned int pending_work;

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 806514d76d8dc..9aafb949fa100 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2449,7 +2449,7 @@ static void __perf_event_disable(struct perf_event *event,
* hold the top-level event's child_mutex, so any descendant that
* goes to exit will block in perf_event_exit_event().
*
- * When called from perf_pending_irq it's OK because event->ctx
+ * When called from perf_pending_disable it's OK because event->ctx
* is the current context on this CPU and preemption is disabled,
* hence we can't get into perf_event_task_sched_out for this context.
*/
@@ -2489,7 +2489,7 @@ EXPORT_SYMBOL_GPL(perf_event_disable);
void perf_event_disable_inatomic(struct perf_event *event)
{
event->pending_disable = 1;
- irq_work_queue(&event->pending_irq);
+ irq_work_queue(&event->pending_disable_irq);
}

#define MAX_INTERRUPTS (~0ULL)
@@ -5175,6 +5175,7 @@ static void perf_addr_filters_splice(struct perf_event *event,
static void _free_event(struct perf_event *event)
{
irq_work_sync(&event->pending_irq);
+ irq_work_sync(&event->pending_disable_irq);

unaccount_event(event);

@@ -6711,7 +6712,7 @@ static void perf_sigtrap(struct perf_event *event)
/*
* Deliver the pending work in-event-context or follow the context.
*/
-static void __perf_pending_irq(struct perf_event *event)
+static void __perf_pending_disable(struct perf_event *event)
{
int cpu = READ_ONCE(event->oncpu);

@@ -6749,11 +6750,26 @@ static void __perf_pending_irq(struct perf_event *event)
* irq_work_queue(); // FAILS
*
* irq_work_run()
- * perf_pending_irq()
+ * perf_pending_disable()
*
* But the event runs on CPU-B and wants disabling there.
*/
- irq_work_queue_on(&event->pending_irq, cpu);
+ irq_work_queue_on(&event->pending_disable_irq, cpu);
+}
+
+static void perf_pending_disable(struct irq_work *entry)
+{
+ struct perf_event *event = container_of(entry, struct perf_event, pending_disable_irq);
+ int rctx;
+
+ /*
+ * If we 'fail' here, that's OK, it means recursion is already disabled
+ * and we won't recurse 'further'.
+ */
+ rctx = perf_swevent_get_recursion_context();
+ __perf_pending_disable(event);
+ if (rctx >= 0)
+ perf_swevent_put_recursion_context(rctx);
}

static void perf_pending_irq(struct irq_work *entry)
@@ -6776,8 +6792,6 @@ static void perf_pending_irq(struct irq_work *entry)
perf_event_wakeup(event);
}

- __perf_pending_irq(event);
-
if (rctx >= 0)
perf_swevent_put_recursion_context(rctx);
}
@@ -9566,7 +9580,7 @@ static int __perf_event_overflow(struct perf_event *event,
WARN_ON_ONCE(!atomic_long_inc_not_zero(&event->refcount));
task_work_add(current, &event->pending_task, TWA_RESUME);
if (in_nmi())
- irq_work_queue(&event->pending_irq);
+ irq_work_queue(&event->pending_disable_irq);
} else if (event->attr.exclude_kernel && valid_sample) {
/*
* Should not be able to return to user space without
@@ -11906,6 +11920,7 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,

init_waitqueue_head(&event->waitq);
init_irq_work(&event->pending_irq, perf_pending_irq);
+ event->pending_disable_irq = IRQ_WORK_INIT_HARD(perf_pending_disable);
init_task_work(&event->pending_task, perf_pending_task);

mutex_init(&event->mmap_mutex);
--
2.43.0