[Ocfs2-tools-devel] [PATCH] ocfs2_controld: Handle additional mounts racing umount(2).

[Joel Becker]

ocfs2_controld only allows one MOUNT/UNMOUNT operation at a time.
Racing operations will receive EBUSY.

Well, if the kernel is unmounting while an additional mount is in
progress, the daemon won't clean up after a failed additional mount.

mount /dev/sdb1 /ocfs2
mount /dev/sdb1 /ocfs3
				umount /ocfs2
				# Gets there first, umount(2) happens.
				# ->put_super(7) calls ocfs2_hb_ctl,
				# which gets -EBUSY from
				# o2cb_group_leave().  The filesystem is
				# no longer mounted in the kernel.

The solution is to clear the ms_additional flag when we notice this
race.  The daemon, seeing it is about to send EBUSY to the unmount,
clears ms_additional on the mount of /ocfs3.  Then, when that mount
fails, it knows to exit the group.

Signed-off-by: Joel Becker <joel.becker at oracle.com>
---
 ocfs2_controld/mount.c |   25 ++++++++++++++++++++++++-
 1 files changed, 24 insertions(+), 1 deletions(-)

diff --git a/ocfs2_controld/mount.c b/ocfs2_controld/mount.c
index 11c3e08..36459d1 100644
--- a/ocfs2_controld/mount.c
+++ b/ocfs2_controld/mount.c
@@ -821,7 +821,30 @@ int remove_mount(int ci, int fd, const char *uuid, const char *service)
 	if (mg->mg_ms_in_progress) {
 		fill_error(&mg_error, EBUSY,
 			   "Another mount is in progress");
-		goto out;;
+
+		/*
+		 * If the service we're removing has ms_additional set, it
+		 * must be the filesystem service.  That means the
+		 * in_progress service is an additional real mount, but
+		 * the kernel is no longer mounted.
+		 *
+		 * As such, the in-progress service is now a new mount, and
+		 * we clear the ms_addditional flag.  It will succeed or
+		 * fail as a new mount.
+		 */
+		if (ms->ms_additional) {
+			if (ms != mg->mg_ms_in_progress)
+				log_error("Somehow ms_additional was set "
+					  "even though the in-progress "
+					  "mount isn't the filesystem "
+					  "(group %s, removing %s, "
+					  "in-progress %s",
+					  mg->mg_uuid, ms->ms_service,
+					  mg->mg_ms_in_progress->ms_service);
+			ms->ms_additional = 0;
+		}
+
+		goto out;
 	}
 
 	if ((mg->mg_mount_ci != -1) ||
-- 
1.5.6.3


-- 

Life's Little Instruction Book #510

	"Count your blessings."

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127