Commit c64cd6e3 authored by Al Viro's avatar Al Viro
Browse files

reimplement path_mountpoint() with less magic 



... and get rid of a bunch of bugs in it.  Background:
the reason for path_mountpoint() is that umount() really doesn't
want attempts to revalidate the root of what it's trying to umount.
The thing we want to avoid actually happen from complete_walk();
solution was to do something parallel to normal path_lookupat()
and it both went overboard and got the boilerplate subtly
(and not so subtly) wrong.

A better solution is to do pretty much what the normal path_lookupat()
does, but instead of complete_walk() do unlazy_walk().  All it takes
to avoid that ->d_weak_revalidate() call...  mountpoint_last() goes
away, along with everything it got wrong, and so does the magic around
LOOKUP_NO_REVAL.

Another source of bugs is that when we traverse mounts at the final
location (and we need to do that - umount . expects to get whatever's
overmounting ., if any, out of the lookup) we really ought to take
care of ->d_manage() - as it is, manual umount of autofs automount
in progress can lead to unpleasant surprises for the daemon.  Easily
solved by using handle_lookup_down() instead of follow_mount().

Tested-by: default avatarIan Kent <raven@themaw.net>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 1edc8eb2

fs/namei.c

+12 −77
Original line number Diff line number Diff line
@@ -1649,7 +1649,6 @@ again: 
	if (IS_ERR(dentry))

		return dentry;

	if (unlikely(!d_in_lookup(dentry))) {

		if (!(flags & LOOKUP_NO_REVAL)) {

		int error = d_revalidate(dentry, flags);

		if (unlikely(error <= 0)) {

			if (!error) {
@@ -1660,7 +1659,6 @@ again: 
			dput(dentry);

			dentry = ERR_PTR(error);

		}

		}

	} else {

		old = inode->i_op->lookup(inode, dentry, flags);

		d_lookup_done(dentry);
@@ -2617,72 +2615,6 @@ int user_path_at_empty(int dfd, const char __user *name, unsigned flags, 
}

EXPORT_SYMBOL(user_path_at_empty);



/**

 * mountpoint_last - look up last component for umount

 * @nd:   pathwalk nameidata - currently pointing at parent directory of "last"

 *

 * This is a special lookup_last function just for umount. In this case, we

 * need to resolve the path without doing any revalidation.

 *

 * The nameidata should be the result of doing a LOOKUP_PARENT pathwalk. Since

 * mountpoints are always pinned in the dcache, their ancestors are too. Thus,

 * in almost all cases, this lookup will be served out of the dcache. The only

 * cases where it won't are if nd->last refers to a symlink or the path is

 * bogus and it doesn't exist.

 *

 * Returns:

 * -error: if there was an error during lookup. This includes -ENOENT if the

 *         lookup found a negative dentry.

 *

 * 0:      if we successfully resolved nd->last and found it to not to be a

 *         symlink that needs to be followed.

 *

 * 1:      if we successfully resolved nd->last and found it to be a symlink

 *         that needs to be followed.

 */

static int

mountpoint_last(struct nameidata *nd)

{

	int error = 0;

	struct dentry *dir = nd->path.dentry;

	struct path path;



	/* If we're in rcuwalk, drop out of it to handle last component */

	if (nd->flags & LOOKUP_RCU) {

		if (unlazy_walk(nd))

			return -ECHILD;

	}



	nd->flags &= ~LOOKUP_PARENT;



	if (unlikely(nd->last_type != LAST_NORM)) {

		error = handle_dots(nd, nd->last_type);

		if (error)

			return error;

		path.dentry = dget(nd->path.dentry);

	} else {

		path.dentry = d_lookup(dir, &nd->last);

		if (!path.dentry) {

			/*

			 * No cached dentry. Mounted dentries are pinned in the

			 * cache, so that means that this dentry is probably

			 * a symlink or the path doesn't actually point

			 * to a mounted dentry.

			 */

			path.dentry = lookup_slow(&nd->last, dir,

					     nd->flags | LOOKUP_NO_REVAL);

			if (IS_ERR(path.dentry))

				return PTR_ERR(path.dentry);

		}

	}

	if (d_flags_negative(smp_load_acquire(&path.dentry->d_flags))) {

		dput(path.dentry);

		return -ENOENT;

	}

	path.mnt = nd->path.mnt;

	return step_into(nd, &path, 0, d_backing_inode(path.dentry), 0);

}



/**

 * path_mountpoint - look up a path to be umounted

 * @nd:		lookup context
@@ -2699,14 +2631,17 @@ path_mountpoint(struct nameidata *nd, unsigned flags, struct path *path) 
	int err;



	while (!(err = link_path_walk(s, nd)) &&

		(err = mountpoint_last(nd)) > 0) {

		(err = lookup_last(nd)) > 0) {

		s = trailing_symlink(nd);

	}

	if (!err && (nd->flags & LOOKUP_RCU))

		err = unlazy_walk(nd);

	if (!err)

		err = handle_lookup_down(nd);

	if (!err) {

		*path = nd->path;

		nd->path.mnt = NULL;

		nd->path.dentry = NULL;

		follow_mount(path);

	}

	terminate_walk(nd);

	return err;

fs/nfs/nfstrace.h

+0 −2
Original line number Diff line number Diff line
@@ -206,7 +206,6 @@ TRACE_DEFINE_ENUM(LOOKUP_AUTOMOUNT); 
TRACE_DEFINE_ENUM(LOOKUP_PARENT);

TRACE_DEFINE_ENUM(LOOKUP_REVAL);

TRACE_DEFINE_ENUM(LOOKUP_RCU);

TRACE_DEFINE_ENUM(LOOKUP_NO_REVAL);

TRACE_DEFINE_ENUM(LOOKUP_OPEN);

TRACE_DEFINE_ENUM(LOOKUP_CREATE);

TRACE_DEFINE_ENUM(LOOKUP_EXCL);
@@ -224,7 +223,6 @@ TRACE_DEFINE_ENUM(LOOKUP_DOWN); 
			{ LOOKUP_PARENT, "PARENT" }, \

			{ LOOKUP_REVAL, "REVAL" }, \

			{ LOOKUP_RCU, "RCU" }, \

			{ LOOKUP_NO_REVAL, "NO_REVAL" }, \

			{ LOOKUP_OPEN, "OPEN" }, \

			{ LOOKUP_CREATE, "CREATE" }, \

			{ LOOKUP_EXCL, "EXCL" }, \

include/linux/namei.h

+0 −1
Original line number Diff line number Diff line
@@ -34,7 +34,6 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND}; 


/* internal use only */

#define LOOKUP_PARENT		0x0010

#define LOOKUP_NO_REVAL		0x0080

#define LOOKUP_JUMPED		0x1000

#define LOOKUP_ROOT		0x2000

#define LOOKUP_ROOT_GRABBED	0x0008

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