dcache: Reduce the scope of i_lock in d_splice_alias (a03e283b) · Commits · 戴 / test

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:

"Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by:

Al Viro <viro@zeniv.linux.org.uk>

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 @@ out_unalias:
		__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);

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