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authorIan Kent <raven@themaw.net>2022-07-08 09:43:18 +0800
committerakpm <akpm@linux-foundation.org>2022-07-17 17:31:42 -0700
commitba97a0a3a31a2451607ebf601c0b7c4b1322ce9a (patch)
tree7e86630bebba7fb0b7e1e7a6aad5569bce5c594b /fs/autofs
parenta4a87303874c1a7d49cc18a8fe33676b0002ffbf (diff)
autofs: add comment about autofs_mountpoint_changed()
The function autofs_mountpoint_changed() is unusual, add a comment about two cases for which it is needed. Link: https://lkml.kernel.org/r/165724459804.30914.10974834416046555127.stgit@donald.themaw.net Signed-off-by: Ian Kent <raven@themaw.net> Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: David Howells <dhowells@redhat.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'fs/autofs')
-rw-r--r--fs/autofs/root.c23
1 files 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;