[PATCH] drbd: make drbd_adm_detach() interruptible

[Philipp Reisner <philipp.reisner@linbit.com>]

If a backing device suddenly ceases delivering I/O completions, and in
reaction, the user issues a `drbdsetup detach`, the operation will
hang when it tries to write internal meta-data.

The user should have used `drbdsetup --force detach`, but it is too
late. There was no way to interrupt the hanging drbdsetup detach.

Improve the situation by making detach operations interruptible.
---
 drbd/drbd_actlog.c |  5 ++++-
 drbd/drbd_int.h    |  1 +
 drbd/drbd_state.c  | 29 +++++++++++++++++++++++++++--
 3 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/drbd/drbd_actlog.c b/drbd/drbd_actlog.c
index bc09dee2f..d6ba168ac 100644
--- a/drbd/drbd_actlog.c
+++ b/drbd/drbd_actlog.c
@@ -74,7 +74,10 @@ void wait_until_done_or_force_detached(struct drbd_device *device, struct drbd_b
 		dt = MAX_SCHEDULE_TIMEOUT;
 
 	dt = wait_event_timeout(device->misc_wait,
-			*done || test_bit(FORCE_DETACH, &device->flags), dt);
+			*done ||
+			test_bit(FORCE_DETACH, &device->flags) ||
+			test_bit(INTERRUPT_DETACH, &device->flags),
+			dt);
 	if (dt == 0) {
 		drbd_err(device, "meta-data IO operation timed out\n");
 		drbd_handle_io_error(device, DRBD_FORCE_DETACH);
diff --git a/drbd/drbd_int.h b/drbd/drbd_int.h
index 0ebd79091..8ea752edd 100644
--- a/drbd/drbd_int.h
+++ b/drbd/drbd_int.h
@@ -521,6 +521,7 @@ enum device_flag {
 	MD_NO_FUA,		/* meta data device does not support barriers,
 				   so don't even try */
 	FORCE_DETACH,		/* Force-detach from local disk, aborting any pending local IO */
+	INTERRUPT_DETACH,	/* Interrupt an ongoing detach operation */
 	NEW_CUR_UUID,		/* Create new current UUID when thawing IO or issuing local IO */
 	__NEW_CUR_UUID,		/* Set NEW_CUR_UUID as soon as state change visible */
 	WRITING_NEW_CUR_UUID,	/* Set while the new current ID gets generated. */
diff --git a/drbd/drbd_state.c b/drbd/drbd_state.c
index be1de8f06..643b2f385 100644
--- a/drbd/drbd_state.c
+++ b/drbd/drbd_state.c
@@ -924,14 +924,39 @@ void state_change_lock(struct drbd_resource *resource, unsigned long *irq_flags,
 	resource->state_change_flags = flags;
 }
 
+/* Interrupt writing meta-data */
+static void interrupt_detach(struct drbd_resource *resource, struct completion *done)
+{
+	struct drbd_device *device;
+	int vnr;
+
+	idr_for_each_entry(&resource->devices, device, vnr) {
+		if (device->disk_state[NOW] == D_DETACHING) {
+			set_bit(INTERRUPT_DETACH, &device->flags);
+			wake_up_all(&device->misc_wait);
+		}
+	}
+
+	wait_for_completion(done);
+
+	idr_for_each_entry(&resource->devices, device, vnr) {
+		if (test_bit(INTERRUPT_DETACH, &device->flags))
+			clear_bit(INTERRUPT_DETACH, &device->flags);
+	}
+}
+
 static void __state_change_unlock(struct drbd_resource *resource, unsigned long *irq_flags, struct completion *done)
 {
 	enum chg_state_flags flags = resource->state_change_flags;
 
 	resource->state_change_flags = 0;
 	write_unlock_irqrestore(&resource->state_rwlock, *irq_flags);
-	if (done && expect(resource, current != resource->worker.task))
-		wait_for_completion(done);
+	if (done && expect(resource, current != resource->worker.task)) {
+		int err = wait_for_completion_interruptible(done);
+
+		if (err == -ERESTARTSYS)
+			interrupt_detach(resource, done);
+	}
 	if ((flags & CS_SERIALIZE) && !(flags & (CS_ALREADY_SERIALIZED | CS_PREPARE)))
 		up(&resource->state_sem);
 }
-- 
2.45.2