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Commit a03e283b authored by Eric W. Biederman's avatar Eric W. Biederman Committed by Al Viro
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dcache: Reduce the scope of i_lock in d_splice_alias 



i_lock is only needed until __d_find_any_alias calls dget on the alias
dentry.  After that the reference to new ensures that dentry_kill and
d_delete will not remove the inode from the dentry, and remove the
dentry from the inode->d_entry list.

The inode i_lock came to be held over the the __d_move calls in
d_splice_alias through a series of introduction of locks with
increasing smaller scope.  First it was the dcache_lock, then
it was the dcache_inode_lock, and finally inode->i_lock.

Furthermore inode->i_lock is not held over any other calls
to d_move or __d_move so it can not provide any meaningful
rename protection.

Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent cde93be4

fs/dcache.c

+3 −4
Original line number Diff line number Diff line
@@ -2718,7 +2718,7 @@ struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2) 
 * This helper attempts to cope with remotely renamed directories

 *

 * It assumes that the caller is already holding

 * dentry->d_parent->d_inode->i_mutex, inode->i_lock and rename_lock

 * dentry->d_parent->d_inode->i_mutex, and rename_lock

 *

 * Note: If ever the locking in lock_rename() changes, then please

 * remember to update this too...
@@ -2744,7 +2744,6 @@ static int __d_unalias(struct inode *inode, 
	__d_move(alias, dentry, false);

	ret = 0;

out_err:

	spin_unlock(&inode->i_lock);

	if (m2)

		mutex_unlock(m2);

	if (m1)
@@ -2790,10 +2789,11 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry) 
	if (S_ISDIR(inode->i_mode)) {

		struct dentry *new = __d_find_any_alias(inode);

		if (unlikely(new)) {

			/* The reference to new ensures it remains an alias */

			spin_unlock(&inode->i_lock);

			write_seqlock(&rename_lock);

			if (unlikely(d_ancestor(new, dentry))) {

				write_sequnlock(&rename_lock);

				spin_unlock(&inode->i_lock);

				dput(new);

				new = ERR_PTR(-ELOOP);

				pr_warn_ratelimited(
@@ -2812,7 +2812,6 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry) 
			} else {

				__d_move(new, dentry, false);

				write_sequnlock(&rename_lock);

				spin_unlock(&inode->i_lock);

				security_d_instantiate(new, inode);

			}

			iput(inode);