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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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Oleg Nesterov 2013-07-26 17:12:56 +02:00 committed by Steven Rostedt
parent 8c4f3c3fa9
commit 776164c1fa
1 changed files with 23 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

71
fs/debugfs/inode.c
View File

@ -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;
}
/*
* 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);
up:
if (!__debugfs_remove(child, parent))
simple_release_fs(&debugfs_mount, &debugfs_mount_count);
}
parent = dentry->d_parent;
mutex_lock(&parent->d_inode->i_mutex);
__debugfs_remove(dentry, parent);
mutex_unlock(&parent->d_inode->i_mutex);
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;
}
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);