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Commit 68f0d9d9 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

vfs: make d_path() get the root path under RCU 



This avoids the spinlocks and refcounts in the d_path() sequence too
(used by /proc and various other entities).  See commit 8b19e341 for
the equivalent getcwd() system call path.

And unlike getcwd(), d_path() doesn't copy the result to user space, so
I don't need to fear _that_ particular bug happening again.

Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3272c544

fs/dcache.c

+14 −2
Original line number Diff line number Diff line
@@ -2869,6 +2869,16 @@ static int prepend_unreachable(char **buffer, int *buflen) 
	return prepend(buffer, buflen, "(unreachable)", 13);

}



static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)

{

	unsigned seq;



	do {

		seq = read_seqcount_begin(&fs->seq);

		*root = fs->root;

	} while (read_seqcount_retry(&fs->seq, seq));

}



/**

 * d_path - return the path of a dentry

 * @path: path to report
@@ -2901,13 +2911,15 @@ char *d_path(const struct path *path, char *buf, int buflen) 
	if (path->dentry->d_op && path->dentry->d_op->d_dname)

		return path->dentry->d_op->d_dname(path->dentry, buf, buflen);



	get_fs_root(current->fs, &root);

	rcu_read_lock();

	get_fs_root_rcu(current->fs, &root);

	br_read_lock(&vfsmount_lock);

	error = path_with_deleted(path, &root, &res, &buflen);

	br_read_unlock(&vfsmount_lock);

	rcu_read_unlock();



	if (error < 0)

		res = ERR_PTR(error);

	path_put(&root);

	return res;

}

EXPORT_SYMBOL(d_path);