[PATCH v2] coresight: Fix possible deadlock in coresight_panic_cb

[Sean Anderson <sean.anderson@linux.dev>]

coresight_panic_cb is called with interrupts disabled during panics.
However, bus_for_each_dev calls bus_to_subsys which takes
bus_kset->list_lock without disabling IRQs. This will cause a deadlock
if a panic occurs while one of the other coresight functions that uses
bus_for_each_dev is running.

Maintain a separate list of coresight devices to access during a panic.

Fixes: 46006ceb5d02 ("coresight: core: Add provision for panic callbacks")
Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
---

Changes in v2:
- Add a comment describing csdev_lock/list
- Consolidate list removal in coresight_device_release

 drivers/hwtracing/coresight/coresight-core.c | 43 +++++++++++---------
 include/linux/coresight.h                    |  1 +
 2 files changed, 25 insertions(+), 19 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index fa758cc21827..4e28e56f2e30 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -1042,10 +1042,19 @@ static void coresight_clear_default_sink(struct coresight_device *csdev)
 	}
 }
 
+/*
+ * Dedicated list of devices for use by during panic (which may occur with
+ * interrupts disabled).
+ */
+static DEFINE_SPINLOCK(csdev_lock);
+static LIST_HEAD(csdev_list);
+
 static void coresight_device_release(struct device *dev)
 {
 	struct coresight_device *csdev = to_coresight_device(dev);
 
+	scoped_guard(spinlock_irq, &csdev_lock)
+		list_del(&csdev->csdev_list);
 	fwnode_handle_put(csdev->dev.fwnode);
 	free_percpu(csdev->perf_sink_id_map.cpu_map);
 	kfree(csdev);
@@ -1357,6 +1366,10 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 			goto err_out;
 		}
 	}
+
+	scoped_guard(spinlock_irq, &csdev_lock)
+		list_add(&csdev->csdev_list, &csdev_list);
+
 	/*
 	 * Make sure the device registration and the connection fixup
 	 * are synchronised, so that we don't see uninitialised devices
@@ -1563,28 +1576,20 @@ const struct bus_type coresight_bustype = {
 	.name	= "coresight",
 };
 
-static int coresight_panic_sync(struct device *dev, void *data)
-{
-	int mode;
-	struct coresight_device *csdev;
-
-	/* Run through panic sync handlers for all enabled devices */
-	csdev = container_of(dev, struct coresight_device, dev);
-	mode = coresight_get_mode(csdev);
-
-	if ((mode == CS_MODE_SYSFS) || (mode == CS_MODE_PERF)) {
-		if (panic_ops(csdev))
-			panic_ops(csdev)->sync(csdev);
-	}
-
-	return 0;
-}
-
 static int coresight_panic_cb(struct notifier_block *self,
 			       unsigned long v, void *p)
 {
-	bus_for_each_dev(&coresight_bustype, NULL, NULL,
-				 coresight_panic_sync);
+	struct coresight_device *csdev;
+
+	guard(spinlock)(&csdev_lock);
+	list_for_each_entry(csdev, &csdev_list, csdev_list) {
+		/* Run through panic sync handlers for all enabled devices */
+		int mode = coresight_get_mode(csdev);
+
+		if ((mode == CS_MODE_SYSFS || mode == CS_MODE_PERF) &&
+		    panic_ops(csdev))
+			panic_ops(csdev)->sync(csdev);
+	}
 
 	return 0;
 }
diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index 4ac65c68bbf4..a5e62ebd03b5 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -302,6 +302,7 @@ struct coresight_device {
 	/* system configuration and feature lists */
 	struct list_head feature_csdev_list;
 	struct list_head config_csdev_list;
+	struct list_head csdev_list;
 	raw_spinlock_t cscfg_csdev_lock;
 	void *active_cscfg_ctxt;
 };
-- 
2.35.1.1320.gc452695387.dirty