Commit d41efb52 authored by Al Viro's avatar Al Viro
Browse files

fs/namei.c: pull positivity check into follow_managed() 



There are 4 callers; two proceed to check if result is positive and
fail with ENOENT if it isn't; one (in handle_lookup_down()) is
guaranteed to yield positive and one (in lookup_fast()) is _preceded_
by positivity check.

However, follow_managed() on a negative dentry is a (fairly cheap)
no-op on anything other than autofs.  And negative autofs dentries
are never hashed, so lookup_fast() is not going to run into one
of those.  Moreover, successful follow_managed() on a _positive_
dentry never yields a negative one (and we significantly rely upon
that in callers of lookup_fast()).

In other words, we can easily transpose the positivity check and
the call of follow_managed() in lookup_fast().  And that allows
to fold the positivity check *into* follow_managed(), simplifying
life for the code downstream of its calls.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 3e5aeec0

fs/namei.c

+11 −23
Original line number Diff line number Diff line
@@ -1206,25 +1206,25 @@ static int follow_automount(struct path *path, struct nameidata *nd, 
 * - Flagged as automount point

 *

 * This may only be called in refwalk mode.

 * On success path->dentry is known positive.

 *

 * Serialization is taken care of in namespace.c

 */

static int follow_managed(struct path *path, struct nameidata *nd)

{

	struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */

	unsigned managed;

	unsigned flags;

	bool need_mntput = false;

	int ret = 0;



	/* Given that we're not holding a lock here, we retain the value in a

	 * local variable for each dentry as we look at it so that we don't see

	 * the components of that value change under us */

	while (managed = READ_ONCE(path->dentry->d_flags),

	       managed &= DCACHE_MANAGED_DENTRY,

	       unlikely(managed != 0)) {

	while (flags = READ_ONCE(path->dentry->d_flags),

	       unlikely(flags & DCACHE_MANAGED_DENTRY)) {

		/* Allow the filesystem to manage the transit without i_mutex

		 * being held. */

		if (managed & DCACHE_MANAGE_TRANSIT) {

		if (flags & DCACHE_MANAGE_TRANSIT) {

			BUG_ON(!path->dentry->d_op);

			BUG_ON(!path->dentry->d_op->d_manage);

			ret = path->dentry->d_op->d_manage(path, false);
@@ -1233,7 +1233,7 @@ static int follow_managed(struct path *path, struct nameidata *nd) 
		}



		/* Transit to a mounted filesystem. */

		if (managed & DCACHE_MOUNTED) {

		if (flags & DCACHE_MOUNTED) {

			struct vfsmount *mounted = lookup_mnt(path);

			if (mounted) {

				dput(path->dentry);
@@ -1252,7 +1252,7 @@ static int follow_managed(struct path *path, struct nameidata *nd) 
		}



		/* Handle an automount point */

		if (managed & DCACHE_NEED_AUTOMOUNT) {

		if (flags & DCACHE_NEED_AUTOMOUNT) {

			ret = follow_automount(path, nd, &need_mntput);

			if (ret < 0)

				break;
@@ -1265,10 +1265,12 @@ static int follow_managed(struct path *path, struct nameidata *nd) 


	if (need_mntput && path->mnt == mnt)

		mntput(path->mnt);

	if (ret == -EISDIR || !ret)

		ret = 1;

	if (need_mntput)

		nd->flags |= LOOKUP_JUMPED;

	if (ret == -EISDIR || !ret)

		ret = 1;

	if (ret > 0 && unlikely(d_flags_negative(flags)))

		ret = -ENOENT;

	if (unlikely(ret < 0))

		path_put_conditional(path, nd);

	return ret;
@@ -1617,10 +1619,6 @@ static int lookup_fast(struct nameidata *nd, 
		dput(dentry);

		return status;

	}

	if (unlikely(d_is_negative(dentry))) {

		dput(dentry);

		return -ENOENT;

	}



	path->mnt = mnt;

	path->dentry = dentry;
@@ -1807,11 +1805,6 @@ static int walk_component(struct nameidata *nd, int flags) 
		if (unlikely(err < 0))

			return err;



		if (unlikely(d_is_negative(path.dentry))) {

			path_to_nameidata(&path, nd);

			return -ENOENT;

		}



		seq = 0;	/* we are already out of RCU mode */

		inode = d_backing_inode(path.dentry);

	}
@@ -3352,11 +3345,6 @@ static int do_last(struct nameidata *nd, 
	if (unlikely(error < 0))

		return error;



	if (unlikely(d_is_negative(path.dentry))) {

		path_to_nameidata(&path, nd);

		return -ENOENT;

	}



	/*

	 * create/update audit record if it already exists.

	 */

include/linux/dcache.h

+5 −0
Original line number Diff line number Diff line
@@ -440,6 +440,11 @@ static inline bool d_is_negative(const struct dentry *dentry) 
	return d_is_miss(dentry);

}



static inline bool d_flags_negative(unsigned flags)

{

	return (flags & DCACHE_ENTRY_TYPE) == DCACHE_MISS_TYPE;

}



static inline bool d_is_positive(const struct dentry *dentry)

{

	return !d_is_negative(dentry);

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