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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 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>
This commit is contained in:
Ian Kent 2022-07-08 09:43:18 +08:00 committed by akpm
parent a4a8730387
commit ba97a0a3a3
1 changed files with 20 additions and 3 deletions
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23
fs/autofs/root.c
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@ -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;