The patch titled
Subject: autofs: add comment about autofs_mountpoint_changed()
has been added to the -mm mm-nonmm-unstable branch. Its filename is
autofs-add-comment-about-autofs_mountpoint_changed.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/autofs-add-comment-about-autofs_mountpoint_changed.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Ian Kent <raven@xxxxxxxxxx>
Subject: autofs: add comment about autofs_mountpoint_changed()
Date: Fri, 08 Jul 2022 09:43:18 +0800
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@xxxxxxxxxxxxxxxxx
Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/autofs/root.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
--- a/fs/autofs/root.c~autofs-add-comment-about-autofs_mountpoint_changed
+++ a/fs/autofs/root.c
@@ -291,9 +291,26 @@ static struct dentry *autofs_mountpoint_
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;
_
Patches currently in -mm which might be from raven@xxxxxxxxxx are
autofs-use-inode-permission-method-for-write-access.patch
autofs-make-dentry-info-count-consistent.patch
autofs-use-dentry-info-count-instead-of-simple_empty.patch
autofs-add-comment-about-autofs_mountpoint_changed.patch
autofs-remove-unused-ino-field-inode.patch
