xfs: convey filesystem unmount events to the health monitor

In xfs_healthmon_unmount, send events to xfs_healer so that it knows
that nothing further can be done for the filesystem.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_fs.h

@@ -1014,6 +1014,9 @@ struct xfs_rtgroup_geometry {
 #define XFS_HEALTH_MONITOR_TYPE_RUNNING		(0)
 #define XFS_HEALTH_MONITOR_TYPE_LOST		(1)
 
+/* filesystem was unmounted */
+#define XFS_HEALTH_MONITOR_TYPE_UNMOUNT		(2)
+
 /* lost events */
 struct xfs_health_monitor_lost {
 	__u64	count;

fs/xfs/xfs_healthmon.c

@@ -90,6 +90,7 @@ xfs_healthmon_put(
 			kfree(event);
 		}
 
+		kfree(hm->unmount_event);
 		kfree(hm->buffer);
 		mutex_destroy(&hm->lock);
 		kfree_rcu_mightsleep(hm);
@@ -166,6 +167,7 @@ xfs_healthmon_merge_events(
 
 	switch (existing->type) {
 	case XFS_HEALTHMON_RUNNING:
+	case XFS_HEALTHMON_UNMOUNT:
 		/* should only ever be one of these events anyway */
 		return false;
 
@@ -307,7 +309,10 @@ xfs_healthmon_push(
 	return error;
 }
 
-/* Detach the xfs mount from this healthmon instance. */
+/*
+ * Report that the filesystem is being unmounted, then detach the xfs mount
+ * from this healthmon instance.
+ */
 void
 xfs_healthmon_unmount(
 	struct xfs_mount		*mp)
@@ -317,6 +322,17 @@ xfs_healthmon_unmount(
 	if (!hm)
 		return;
 
+	trace_xfs_healthmon_report_unmount(hm);
+
+	/*
+	 * Insert the unmount notification at the start of the event queue so
+	 * that userspace knows the filesystem went away as soon as possible.
+	 * There's nothing actionable for userspace after an unmount.  Once
+	 * we've inserted the unmount event, hm no longer owns that event.
+	 */
+	__xfs_healthmon_insert(hm, hm->unmount_event);
+	hm->unmount_event = NULL;
+
 	xfs_healthmon_detach(hm);
 	xfs_healthmon_put(hm);
 }
@@ -713,6 +729,20 @@ xfs_ioc_health_monitor(
 	running_event->domain = XFS_HEALTHMON_MOUNT;
 	__xfs_healthmon_insert(hm, running_event);
 
+	/*
+	 * Preallocate the unmount event so that we can't fail to notify the
+	 * filesystem later.  This is key for triggering fast exit of the
+	 * xfs_healer daemon.
+	 */
+	hm->unmount_event = kzalloc(sizeof(struct xfs_healthmon_event),
+			GFP_NOFS);
+	if (!hm->unmount_event) {
+		ret = -ENOMEM;
+		goto out_hm;
+	}
+	hm->unmount_event->type = XFS_HEALTHMON_UNMOUNT;
+	hm->unmount_event->domain = XFS_HEALTHMON_MOUNT;
+
 	/*
 	 * Try to attach this health monitor to the xfs_mount.  The monitor is
 	 * considered live and will receive events if this succeeds.

fs/xfs/xfs_healthmon.h

@@ -34,6 +34,9 @@ struct xfs_healthmon {
 	struct xfs_healthmon_event	*first_event;
 	struct xfs_healthmon_event	*last_event;
 
+	/* preallocated event for unmount */
+	struct xfs_healthmon_event	*unmount_event;
+
 	/* number of events in the list */
 	unsigned int			events;
 
@@ -67,6 +70,7 @@ void xfs_healthmon_unmount(struct xfs_mount *mp);
 enum xfs_healthmon_type {
 	XFS_HEALTHMON_RUNNING,	/* monitor running */
 	XFS_HEALTHMON_LOST,	/* message lost */
+	XFS_HEALTHMON_UNMOUNT,	/* filesystem is unmounting */
 };
 
 enum xfs_healthmon_domain {

fs/xfs/xfs_trace.h

@@ -6005,14 +6005,18 @@ DEFINE_HEALTHMON_EVENT(xfs_healthmon_read_start);
 DEFINE_HEALTHMON_EVENT(xfs_healthmon_read_finish);
 DEFINE_HEALTHMON_EVENT(xfs_healthmon_release);
 DEFINE_HEALTHMON_EVENT(xfs_healthmon_detach);
+DEFINE_HEALTHMON_EVENT(xfs_healthmon_report_unmount);
 
 #define XFS_HEALTHMON_TYPE_STRINGS \
-	{ XFS_HEALTHMON_LOST,		"lost" }
+	{ XFS_HEALTHMON_LOST,		"lost" }, \
+	{ XFS_HEALTHMON_UNMOUNT,	"unmount" }
 
 #define XFS_HEALTHMON_DOMAIN_STRINGS \
 	{ XFS_HEALTHMON_MOUNT,		"mount" }
 
 TRACE_DEFINE_ENUM(XFS_HEALTHMON_LOST);
+TRACE_DEFINE_ENUM(XFS_HEALTHMON_UNMOUNT);
+
 TRACE_DEFINE_ENUM(XFS_HEALTHMON_MOUNT);
 
 DECLARE_EVENT_CLASS(xfs_healthmon_event_class,