Commit 776164c1 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Steven Rostedt
Browse files

debugfs: debugfs_remove_recursive() must not rely on list_empty(d_subdirs) 

debugfs_remove_recursive() is wrong,

1. it wrongly assumes that !list_empty(d_subdirs) means that this
   dir should be removed.

   This is not that bad by itself, but:

2. if d_subdirs does not becomes empty after __debugfs_remove()
   it gives up and silently fails, it doesn't even try to remove
   other entries.

   However ->d_subdirs can be non-empty because it still has the
   already deleted !debugfs_positive() entries.

3. simple_release_fs() is called even if __debugfs_remove() fails.

Suppose we have

	dir1/
		dir2/
			file2
		file1

and someone opens dir1/dir2/file2.

Now, debugfs_remove_recursive(dir1/dir2) succeeds, and dir1/dir2 goes
away.

But debugfs_remove_recursive(dir1) silently fails and doesn't remove
this directory. Because it tries to delete (the already deleted)
dir1/dir2/file2 again and then fails due to "Avoid infinite loop"
logic.

Test-case:

	#!/bin/sh

	cd /sys/kernel/debug/tracing
	echo 'p:probe/sigprocmask sigprocmask' >> kprobe_events
	sleep 1000 < events/probe/sigprocmask/id &
	echo -n >| kprobe_events

	[ -d events/probe ] && echo "ERR!! failed to rm probe"

And after that it is not possible to create another probe entry.

With this patch debugfs_remove_recursive() skips !debugfs_positive()
files although this is not strictly needed. The most important change
is that it does not try to make ->d_subdirs empty, it simply scans
the whole list(s) recursively and removes as much as possible.

Link: http://lkml.kernel.org/r/20130726151256.GC19472@redhat.com



Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 8c4f3c3f

fs/debugfs/inode.c

+22 −47
Original line number Diff line number Diff line
@@ -533,8 +533,7 @@ EXPORT_SYMBOL_GPL(debugfs_remove); 
 */

void debugfs_remove_recursive(struct dentry *dentry)

{

	struct dentry *child;

	struct dentry *parent;

	struct dentry *child, *next, *parent;



	if (IS_ERR_OR_NULL(dentry))

		return;
@@ -544,61 +543,37 @@ void debugfs_remove_recursive(struct dentry *dentry) 
		return;



	parent = dentry;

 down:

	mutex_lock(&parent->d_inode->i_mutex);

	list_for_each_entry_safe(child, next, &parent->d_subdirs, d_u.d_child) {

		if (!debugfs_positive(child))

			continue;



	while (1) {

		/*

		 * When all dentries under "parent" has been removed,

		 * walk up the tree until we reach our starting point.

		 */

		if (list_empty(&parent->d_subdirs)) {

			mutex_unlock(&parent->d_inode->i_mutex);

			if (parent == dentry)

				break;

			parent = parent->d_parent;

			mutex_lock(&parent->d_inode->i_mutex);

		}

		child = list_entry(parent->d_subdirs.next, struct dentry,

				d_u.d_child);

 next_sibling:



		/*

		 * If "child" isn't empty, walk down the tree and

		 * remove all its descendants first.

		 */

		/* perhaps simple_empty(child) makes more sense */

		if (!list_empty(&child->d_subdirs)) {

			mutex_unlock(&parent->d_inode->i_mutex);

			parent = child;

			mutex_lock(&parent->d_inode->i_mutex);

			continue;

			goto down;

		}

		__debugfs_remove(child, parent);

		if (parent->d_subdirs.next == &child->d_u.d_child) {

			/*

			 * Try the next sibling.

			 */

			if (child->d_u.d_child.next != &parent->d_subdirs) {

				child = list_entry(child->d_u.d_child.next,

						   struct dentry,

						   d_u.d_child);

				goto next_sibling;

 up:

		if (!__debugfs_remove(child, parent))

			simple_release_fs(&debugfs_mount, &debugfs_mount_count);

	}



			/*

			 * Avoid infinite loop if we fail to remove

			 * one dentry.

			 */

	mutex_unlock(&parent->d_inode->i_mutex);

			break;

		}

		simple_release_fs(&debugfs_mount, &debugfs_mount_count);

	child = parent;

	parent = parent->d_parent;

	mutex_lock(&parent->d_inode->i_mutex);



	if (child != dentry) {

		next = list_entry(child->d_u.d_child.next, struct dentry,

					d_u.d_child);

		goto up;

	}



	parent = dentry->d_parent;

	mutex_lock(&parent->d_inode->i_mutex);

	__debugfs_remove(dentry, parent);

	mutex_unlock(&parent->d_inode->i_mutex);

	if (!__debugfs_remove(child, parent))

		simple_release_fs(&debugfs_mount, &debugfs_mount_count);

	mutex_unlock(&parent->d_inode->i_mutex);

}

EXPORT_SYMBOL_GPL(debugfs_remove_recursive);

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