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VFS: allow ->d_manage() to declare -EISDIR in rcu_walk mode. 

In REF-walk mode, ->d_manage can return -EISDIR to indicate
that the dentry is not really a mount trap (or even a mount point)
and that any mounts or any DCACHE_NEED_AUTOMOUNT flag should be
ignored.

RCU-walk mode doesn't currently support this, so if there is a dentry
with DCACHE_NEED_AUTOMOUNT set but which shouldn't be a mount-trap,
lookup_fast() will always drop in REF-walk mode.

With this patch, an -EISDIR from ->d_manage will always cause mounts
and automounts to be ignored, both in REF-walk and RCU-walk.

Bug-fixed-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Ian Kent <raven@themaw.net>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
NeilBrown 2014-08-04 17:06:29 +10:00 committed by Al Viro
parent 7c33d5972c
commit b8faf035ea
2 changed files with 18 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
Documentation/filesystems/vfs.txt
View File

@ -1053,7 +1053,8 @@ struct dentry_operations {
If the 'rcu_walk' parameter is true, then the caller is doing a
pathwalk in RCU-walk mode. Sleeping is not permitted in this mode,
and the caller can be asked to leave it and call again by returning
-ECHILD.
-ECHILD. -EISDIR may also be returned to tell pathwalk to
ignore d_automount or any mounts.
This function is only used if DCACHE_MANAGE_TRANSIT is set on the
dentry being transited from.

25
fs/namei.c
View File

@ -1091,10 +1091,10 @@ int follow_down_one(struct path *path)
}
EXPORT_SYMBOL(follow_down_one);
static inline bool managed_dentry_might_block(struct dentry *dentry)
static inline int managed_dentry_rcu(struct dentry *dentry)
{
return (dentry->d_flags & DCACHE_MANAGE_TRANSIT &&
dentry->d_op->d_manage(dentry, true) < 0);
return (dentry->d_flags & DCACHE_MANAGE_TRANSIT) ?
dentry->d_op->d_manage(dentry, true) : 0;
}
/*
@ -1110,11 +1110,18 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
* Don't forget we might have a non-mountpoint managed dentry
* that wants to block transit.
*/
if (unlikely(managed_dentry_might_block(path->dentry)))
switch (managed_dentry_rcu(path->dentry)) {
case -ECHILD:
default:
return false;
case -EISDIR:
return true;
case 0:
break;
}
if (!d_mountpoint(path->dentry))
return true;
return !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
mounted = __lookup_mnt(path->mnt, path->dentry);
if (!mounted)
@ -1130,7 +1137,8 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
*/
*inode = path->dentry->d_inode;
}
return read_seqretry(&mount_lock, nd->m_seq);
return read_seqretry(&mount_lock, nd->m_seq) &&
!(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
}
static int follow_dotdot_rcu(struct nameidata *nd)
@ -1402,10 +1410,7 @@ static int lookup_fast(struct nameidata *nd,
}
path->mnt = mnt;
path->dentry = dentry;
if (unlikely(!__follow_mount_rcu(nd, path, inode)))
goto unlazy;
if (unlikely(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT))
goto unlazy;
if (likely(__follow_mount_rcu(nd, path, inode)))
return 0;
unlazy:
if (unlazy_walk(nd, dentry))