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Commit b8faf035 authored by NeilBrown's avatar NeilBrown Committed by Al Viro
Browse files

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: default avatarDan Carpenter <dan.carpenter@oracle.com>
Cc: Ian Kent <raven@themaw.net>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 7c33d597

Documentation/filesystems/vfs.txt

+2 −1
Original line number Diff line number Diff line
@@ -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.

fs/namei.c

+16 −11
Original line number Diff line number Diff line
@@ -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))