The function autofs_mountpoint_changed() is unusual, add a comment
about two cases for which it is needed.
Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
---
fs/autofs/root.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
diff --git a/fs/autofs/root.c b/fs/autofs/root.c
index e0fa71eb5c05..ca03c1cae2be 100644
--- a/fs/autofs/root.c
+++ b/fs/autofs/root.c
@@ -291,9 +291,26 @@ static struct dentry *autofs_mountpoint_changed(struct path *path)
struct dentry *dentry = path->dentry;
struct autofs_sb_info *sbi = autofs_sbi(dentry->d_sb);
- /*
- * If this is an indirect mount the dentry could have gone away
- * as a result of an expire and a new one created.
+ /* If this is an indirect mount the dentry could have gone away
+ * and a new one created.
+ *
+ * This is unusual and I can't remember the case for which it
+ * was originally added now. But an example of how this can
+ * happen is an autofs indirect mount that has the "browse"
+ * option set and also has the "symlink" option in the autofs
+ * map entry. In this case the daemon will remove the browse
+ * directory and create a symlink as the mount leaving the
+ * struct path stale.
+ *
+ * Another not so obvious case is when a mount in an autofs
+ * indirect mount that uses the "nobrowse" option is being
+ * expired at the same time as a path walk. If the mount has
+ * been umounted but the mount point directory seen before
+ * becoming unhashed (during a lockless path walk) when a stat
+ * family system call is made the mount won't be re-mounted as
+ * it should. In this case the mount point that's been removed
+ * (by the daemon) will be stale and the a new mount point
+ * dentry created.
*/
if (autofs_type_indirect(sbi->type) && d_unhashed(dentry)) {
struct dentry *parent = dentry->d_parent;
