[PATCH] jfs: makes diUnmount/diMount in jfs_mount_rw atomic

[Oleg Kanatov]

jfs_mount_rw can call diUnmount and then diMount. These calls
change the imap pointer.
In case JFS filesystem is mounted on root (/), between these two
calls there may be calls of function jfs_lookup().
The jfs_lookup() function calls jfs_iget(), which, in its turn,
calls diRead(). The latter references the imap pointer.
That may cause diRead() to refer to a pointer "freed" in
diUnmount().
This commit makes calls diUnmount()/diMount() be atomic so that
nothing will read the imap pointer until the whole remount is
completed.

Signed-off-by: Oleg Kanatov <okanatov@xxxxxxxxx>
---
 fs/jfs/jfs_imap.c  | 2 +-
 fs/jfs/jfs_mount.c | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/jfs/jfs_imap.c b/fs/jfs/jfs_imap.c
index 799d3837e7c2..390cbfce391f 100644
--- a/fs/jfs/jfs_imap.c
+++ b/fs/jfs/jfs_imap.c
@@ -310,8 +310,8 @@ int diRead(struct inode *ip)
 	iagno = INOTOIAG(ip->i_ino);
 
 	/* read the iag */
-	imap = JFS_IP(ipimap)->i_imap;
 	IREAD_LOCK(ipimap, RDWRLOCK_IMAP);
+	imap = JFS_IP(ipimap)->i_imap;
 	rc = diIAGRead(imap, iagno, &mp);
 	IREAD_UNLOCK(ipimap);
 	if (rc) {
diff --git a/fs/jfs/jfs_mount.c b/fs/jfs/jfs_mount.c
index 48d1f70f786c..972b9ff18723 100644
--- a/fs/jfs/jfs_mount.c
+++ b/fs/jfs/jfs_mount.c
@@ -234,12 +234,18 @@ int jfs_mount_rw(struct super_block *sb, int remount)
 
 		truncate_inode_pages(sbi->ipimap->i_mapping, 0);
 		truncate_inode_pages(sbi->ipbmap->i_mapping, 0);
+
+		IWRITE_LOCK(sbi->ipimap, RDWRLOCK_IMAP);
+
 		diUnmount(sbi->ipimap, 1);
 		if ((rc = diMount(sbi->ipimap))) {
+			IWRITE_UNLOCK(sbi->ipimap);
 			jfs_err("jfs_mount_rw: diMount failed!");
 			return rc;
 		}
 
+		IWRITE_UNLOCK(sbi->ipimap);
+
 		dbUnmount(sbi->ipbmap, 1);
 		if ((rc = dbMount(sbi->ipbmap))) {
 			jfs_err("jfs_mount_rw: dbMount failed!");
-- 
2.30.2