[lvm-devel] [PATCH] Retry dm device removal if busy

[Peter Rajnoha]

If a dm device is being opened in parallel while we're
trying to remove it, we'll end up with an error that
the device is busy. This is a legitimate error, but
with udev in play and asynchronous events generated
as a result of using the WATCH udev rule, we can get
into a situation where such failure is very unpleasant.

Let's try the removal a few times then. Though this is
not a complete solution to the problem, let's use this
until we have one.

Peter
---
 libdm/ioctl/libdm-iface.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/libdm/ioctl/libdm-iface.c b/libdm/ioctl/libdm-iface.c
index 816f1e6..e4a3a1f 100644
--- a/libdm/ioctl/libdm-iface.c
+++ b/libdm/ioctl/libdm-iface.c
@@ -1539,11 +1539,14 @@ static const char *_sanitise_message(char *message)
 	return sanitised_message;
 }
 
+#define DM_REMOVE_IOCTL_RETRIES 5
+
 static struct dm_ioctl *_do_dm_ioctl(struct dm_task *dmt, unsigned command,
 				     unsigned repeat_count)
 {
 	struct dm_ioctl *dmi;
 	int ioctl_with_uevent;
+	int retries = DM_REMOVE_IOCTL_RETRIES;
 
 	dmi = _flatten(dmt, repeat_count);
 	if (!dmi) {
@@ -1627,11 +1630,23 @@ static struct dm_ioctl *_do_dm_ioctl(struct dm_task *dmt, unsigned command,
 		  dmt->sector, _sanitise_message(dmt->message),
 		  dmi->data_size);
 #ifdef DM_IOCTLS
+repeat_dm_ioctl:
 	if (ioctl(_control_fd, command, dmi) < 0) {
 		if (errno == ENXIO && ((dmt->type == DM_DEVICE_INFO) ||
 				       (dmt->type == DM_DEVICE_MKNODES) ||
 				       (dmt->type == DM_DEVICE_STATUS)))
 			dmi->flags &= ~DM_EXISTS_FLAG;	/* FIXME */
+		/*
+		 * FIXME: This is a workaround for asynchronous events generated
+		 *        as a result of using the WATCH udev rule with which we
+		 *        have no way of synchronizing. Processing such events in
+		 *        parallel causes devices to be open.
+		 */
+		else if (errno == EBUSY && (dmt->type == DM_DEVICE_REMOVE) && retries--) {
+			log_debug("device-mapper: device is busy, retrying removal");
+			sleep(1);
+			goto repeat_dm_ioctl;
+		}
 		else {
 			if (_log_suppress)
 				log_verbose("device-mapper: %s ioctl "