geom: Make g_waitidle() wait for orphaned providers

This is motivated by the following race in the ZFS zvol code.

When a zvol is created, we create a GEOM-backed zvol, which results in a
/dev/zvol/<zvol path> device file, created by GEOM::dev.  If volmode=dev
is specified, zvol_set_volmode_impl() will wither the GEOM, then create
a device file with the same name.  This sometimes fails because
g_wither_geom() is asynchronous, so we end up trying to create a device
file while the old one still exists.  I want to fix this by adding a
g_waitidle() call to zvol_os_remove_minor().

g_waitidle() is not sufficient: GEOM::dev does not destroy the device
until g_dev_orphan() is called.  (In fact the device destruction is
asynchronous too, but the delist_dev() call is sufficient to address
this race.)  So, I propose modifying g_waitidle() to block until
orphaned providers are processed.

PR:		258766
Reviewed by:	mav, imp, kib
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D55049

1 files changed, 1 insertions, 1 deletions

diff --git a/sys/geom/geom_event.c b/sys/geom/geom_event.c
index ffd46db55416..34649cea5a71 100644
--- a/sys/geom/geom_event.c
+++ b/sys/geom/geom_event.c
@@ -84,7 +84,7 @@ g_waitidle(struct thread *td)
 
 	mtx_lock(&g_eventlock);
 	TSWAIT("GEOM events");
-	while (!TAILQ_EMPTY(&g_events))
+	while (!TAILQ_EMPTY(&g_events) || !TAILQ_EMPTY(&g_doorstep))
 		msleep(&g_pending_events, &g_eventlock, PPAUSE,
 		    "g_waitidle", 0);
 	TSUNWAIT("GEOM events");