Re: [PATCH v3] kcov: move kcov_remote_data to task_struct for RT and remove local_lock

[Tetsuo Handa]

On 2026/05/21 22:06, Alexander Potapenko wrote:
> I think a deadlock is possible if a softirq is delivered while a
> background task is executing kcov_remote_start():

Indeed. Since kcov_remote_start() is called by

  static int vhost_run_work_kthread_list(void *data)
  {
    kcov_remote_start_common(worker->kcov_handle);
    work->fn(work);
    kcov_remote_stop();
  }

and it can be preempted by

  static void usb_giveback_urb_bh(struct work_struct *work)
  {
    static void __usb_hcd_giveback_urb(struct urb *urb)
    {
      kcov_remote_start_usb_softirq((u64)urb->dev->bus->busnum);
      urb->complete(urb);
      kcov_remote_stop_softirq();
    }
  }

, we need to use _irq{save,restore} version. Any other concerns?

 kernel/kcov.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 965c11a75b36..70ce99c3205d 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -897,6 +897,7 @@ void kcov_remote_start(u64 handle)
 	void *area;
 	unsigned int size;
 	int sequence;
+	unsigned long flags;
 
 	/* Don't use in_task() in order to allow consistent checks in RT kernels. */
 	if (in_hardirq() || in_nmi())
@@ -918,10 +919,10 @@ void kcov_remote_start(u64 handle)
 	if (WARN_ON(in_serving_softirq() && t->kcov_softirq))
 		return;
 
-	spin_lock(&kcov_remote_lock);
+	spin_lock_irqsave(&kcov_remote_lock, flags);
 	remote = kcov_remote_find(handle);
 	if (!remote) {
-		spin_unlock(&kcov_remote_lock);
+		spin_unlock_irqrestore(&kcov_remote_lock, flags);
 		return;
 	}
 	kcov_debug("handle = %llx, context: %s\n", handle,
@@ -949,7 +950,7 @@ void kcov_remote_start(u64 handle)
 		area = this_cpu_ptr(&kcov_percpu_data)->irq_area;
 	}
 #endif
-	spin_unlock(&kcov_remote_lock);
+	spin_unlock_irqrestore(&kcov_remote_lock, flags);
 
 	/* Can only happen when CONFIG_PREEMPT_RT=y or in_task(). */
 	if (!area) {
@@ -1044,6 +1045,7 @@ void kcov_remote_stop(void)
 	void *area;
 	unsigned int size;
 	int sequence;
+	unsigned long flags;
 
 	/* Don't use in_task() in order to allow consistent checks in RT kernels. */
 	if (in_hardirq() || in_nmi())
@@ -1084,9 +1086,9 @@ void kcov_remote_stop(void)
 	spin_unlock(&kcov->lock);
 
 	if (IS_ENABLED(CONFIG_PREEMPT_RT) || in_task()) {
-		spin_lock(&kcov_remote_lock);
+		spin_lock_irqsave(&kcov_remote_lock, flags);
 		kcov_remote_area_put(area, size);
-		spin_unlock(&kcov_remote_lock);
+		spin_unlock_irqrestore(&kcov_remote_lock, flags);
 	}
 
 	/* Get in kcov_remote_start(). */