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Subject[PATCH 4/4] autofs: add comment about autofs_mountpoint_changed()
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The function autofs_mountpoint_changed() is unusual, add a comment
about two cases for which it is used.

Signed-off-by: Ian Kent <raven@themaw.net>
---
fs/autofs/root.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/fs/autofs/root.c b/fs/autofs/root.c
index 308cc49aca1d..a972bbaecb46 100644
--- a/fs/autofs/root.c
+++ b/fs/autofs/root.c
@@ -280,9 +280,24 @@ 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 a 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 (pointing to a
+ * local path) 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 and the mount has been umounted but the mount point
+ * directory remains when a stat family system call is made.
+ * In this case the mount point is removed (by the daemon) and
+ * a new mount triggered leading to a stale dentry in the struct
+ * path of the waiting process.
*/
if (autofs_type_indirect(sbi->type) && d_unhashed(dentry)) {
struct dentry *parent = dentry->d_parent;
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