[PATCH] autofs4: tree race fix

For tree mount maps, a call to chdir or chroot, to a directory above the
moint point directories at a certain time during the expire results in the
expire incorrectly thinking the tree is not busy.  This patch adds a check
to see if the filesystem above the tree mount points is busy and also locks
the filesystem during the tree mount expire to prevent the race.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 14 insertions, 2 deletions

diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index 31540a6404d..500425e24fb 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -99,6 +99,10 @@ static int autofs4_check_tree(struct vfsmount *mnt,
         if (!autofs4_can_expire(top, timeout, do_now))
                 return 0;
 
+        /* Is someone visiting anywhere in the tree ? */
+        if (may_umount_tree(mnt))
+                return 0;
+
         spin_lock(&dcache_lock);
 repeat:
         next = this_parent->d_subdirs.next;
@@ -270,10 +274,18 @@ static struct dentry *autofs4_expire(struct super_block *sb,
 
                 /* Case 2: tree mount, expire iff entire tree is not busy */
                 if (!exp_leaves) {
+                        /* Lock the tree as we must expire as a whole */
+                        spin_lock(&sbi->fs_lock);
                         if (autofs4_check_tree(mnt, dentry, timeout, do_now)) {
-                        expired = dentry;
-                        break;
+                                struct autofs_info *inf = autofs4_dentry_ino(dentry);
+
+                                /* Set this flag early to catch sys_chdir and the like */
+                                inf->flags |= AUTOFS_INF_EXPIRING;
+                                spin_unlock(&sbi->fs_lock);
+                                expired = dentry;
+                                break;
                         }
+                        spin_unlock(&sbi->fs_lock);
                 /* Case 3: direct mount, expire individual leaves */
                 } else {
                         expired = autofs4_check_leaves(mnt, dentry, timeout, do_now);