[PATCH libgpiod] gpiosim: defer removal of bank entries when device is not disabled

[Bartosz Golaszewski <brgl@xxxxxxxx>]

From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

Linux kernel commit 8bd76b3d3f3a ("gpio: sim: lock up configfs that an
instantiated device depends on") has uncovered an issue in libgpiosim:
we use reference counting for all objects (to make RAII easier for
bindings) but, with the above change, if the user doesn't explicitly
disable the device before dropping the last reference to a bank object,
the parent device will never get correctly cleaned up.

This is because we remove the hog and line directories in bank's
release() callback unconditionally. With the directories being locked
now, this fails if device is active and then when we eventually call the
device object's release(), we'll end up stuck with leftover bank
directories and never actually clean-up correctly.

Extend the gpiosim device with a list of deferred banks. When releasing
a bank on an active device, defer any actual cleanup until the time the
device gets deactivated which may be triggered by the user explictly or
will happen automatically when the last reference to the device object is
dropped. For inactive devices, there's no functional change.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
---
 tests/gpiosim/gpiosim.c | 66 +++++++++++++++++++++++++++--------------
 1 file changed, 43 insertions(+), 23 deletions(-)

diff --git a/tests/gpiosim/gpiosim.c b/tests/gpiosim/gpiosim.c
index fca6b7f..81bfd57 100644
--- a/tests/gpiosim/gpiosim.c
+++ b/tests/gpiosim/gpiosim.c
@@ -404,12 +404,14 @@ struct gpiosim_dev {
 	int cfs_dir_fd;
 	int sysfs_dir_fd;
 	struct list_head banks;
+	struct list_head deferred_banks;
 };
 
 struct gpiosim_bank {
 	struct refcount refcnt;
 	struct gpiosim_dev *dev;
 	struct list_head siblings;
+	struct list_head deferred;
 	char *item_name;
 	int id;
 	char *chip_name;
@@ -633,6 +635,7 @@ GPIOSIM_API struct gpiosim_dev *gpiosim_dev_new(struct gpiosim_ctx *ctx)
 	memset(dev, 0, sizeof(*dev));
 	refcount_init(&dev->refcnt, dev_release);
 	list_init(&dev->banks);
+	list_init(&dev->deferred_banks);
 	dev->cfs_dir_fd = configfs_fd;
 	dev->sysfs_dir_fd = -1;
 	dev->item_name = item_name;
@@ -826,8 +829,33 @@ GPIOSIM_API int gpiosim_dev_enable(struct gpiosim_dev *dev)
 	return 0;
 }
 
+static void bank_release_finish(struct gpiosim_bank *bank)
+{
+	struct gpiosim_dev *dev = bank->dev;
+	struct gpiosim_line *line, *tmp;
+	char buf[64];
+
+	list_for_each_entry_safe(line, tmp, &bank->lines, siblings) {
+		snprintf(buf, sizeof(buf), "line%u/hog", line->offset);
+		unlinkat(bank->cfs_dir_fd, buf, AT_REMOVEDIR);
+
+		snprintf(buf, sizeof(buf), "line%u", line->offset);
+		unlinkat(bank->cfs_dir_fd, buf, AT_REMOVEDIR);
+
+		list_del(&line->siblings);
+		free(line);
+	}
+
+	close(bank->cfs_dir_fd);
+	unlinkat(dev->cfs_dir_fd, bank->item_name, AT_REMOVEDIR);
+	free(bank->item_name);
+	id_free(bank->id);
+	free(bank);
+}
+
 GPIOSIM_API int gpiosim_dev_disable(struct gpiosim_dev *dev)
 {
+	struct gpiosim_bank *bank, *tmp;
 	int ret;
 
 	if (!dev_check_live(dev))
@@ -837,6 +865,11 @@ GPIOSIM_API int gpiosim_dev_disable(struct gpiosim_dev *dev)
 	if (ret)
 		return ret;
 
+	list_for_each_entry_safe(bank, tmp, &dev->deferred_banks, deferred) {
+		list_del(&bank->deferred);
+		bank_release_finish(bank);
+	}
+
 	dev_close_sysfs_dirs(dev);
 
 	dev->live = false;
@@ -853,32 +886,19 @@ static void bank_release(struct refcount *ref)
 {
 	struct gpiosim_bank *bank = to_gpiosim_bank(ref);
 	struct gpiosim_dev *dev = bank->dev;
-	struct gpiosim_line *line, *tmp;
-	char buf[64];
-
-	list_for_each_entry_safe(line, tmp, &bank->lines, siblings) {
-		snprintf(buf, sizeof(buf), "line%u/hog", line->offset);
-		unlinkat(bank->cfs_dir_fd, buf, AT_REMOVEDIR);
-
-		snprintf(buf, sizeof(buf), "line%u", line->offset);
-		unlinkat(bank->cfs_dir_fd, buf, AT_REMOVEDIR);
-
-		list_del(&line->siblings);
-		free(line);
-	}
 
 	list_del(&bank->siblings);
-	close(bank->cfs_dir_fd);
-	unlinkat(dev->cfs_dir_fd, bank->item_name, AT_REMOVEDIR);
+
+	/*
+	 * If the device is still active, defer removing the bank directories
+	 * until it's disabled. Otherwise, do it now.
+	 */
+	if (dev->live)
+		list_add(&bank->deferred, &dev->deferred_banks);
+	else
+		bank_release_finish(bank);
+
 	gpiosim_dev_unref(dev);
-	if (bank->sysfs_dir_fd >= 0)
-		/* If the device wasn't disabled yet, this fd is still open. */
-		close(bank->sysfs_dir_fd);
-	free(bank->item_name);
-	id_free(bank->id);
-	free(bank->chip_name);
-	free(bank->dev_path);
-	free(bank);
 }
 
 GPIOSIM_API struct gpiosim_bank *gpiosim_bank_new(struct gpiosim_dev *dev)
-- 
2.45.2