e9117a5a4b
Since commit49d200deaa("debugfs: prevent access to removed files' private data"), accesses to a file's private data are protected from concurrent removal by covering all file_operations with a SRCU read section and sychronizing with those before returning from debugfs_remove() by means of synchronize_srcu(). As pointed out by Johannes Berg, there are debugfs files with forever blocking file_operations. Their corresponding SRCU read side sections would block any debugfs_remove() forever as well, even unrelated ones. This results in a livelock. Because a remover can't cancel any indefinite blocking within foreign files, this is a problem. Resolve this by introducing support for more granular protection on a per-file basis. This is implemented by introducing an 'active_users' refcount_t to the per-file struct debugfs_fsdata state. At file creation time, it is set to one and a debugfs_remove() will drop that initial reference. The new debugfs_file_get() and debugfs_file_put(), intended to be used in place of former debugfs_use_file_start() and debugfs_use_file_finish(), increment and decrement it respectively. Once the count drops to zero, debugfs_file_put() will signal a completion which is possibly being waited for from debugfs_remove(). Thus, as long as there is a debugfs_file_get() not yet matched by a corresponding debugfs_file_put() around, debugfs_remove() will block. Actual users of debugfs_use_file_start() and -finish() will get converted to the new debugfs_file_get() and debugfs_file_put() by followup patches. Fixes:49d200deaa("debugfs: prevent access to removed files' private data") Reported-by: Johannes Berg <johannes@sipsolutions.net> Signed-off-by: Nicolai Stange <nicstange@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
29 lines
810 B
C
29 lines
810 B
C
/*
|
|
* internal.h - declarations internal to debugfs
|
|
*
|
|
* Copyright (C) 2016 Nicolai Stange <nicstange@gmail.com>
|
|
*
|
|
* This program is free software; you can redistribute it and/or
|
|
* modify it under the terms of the GNU General Public License version
|
|
* 2 as published by the Free Software Foundation.
|
|
*
|
|
*/
|
|
|
|
#ifndef _DEBUGFS_INTERNAL_H_
|
|
#define _DEBUGFS_INTERNAL_H_
|
|
|
|
struct file_operations;
|
|
|
|
/* declared over in file.c */
|
|
extern const struct file_operations debugfs_noop_file_operations;
|
|
extern const struct file_operations debugfs_open_proxy_file_operations;
|
|
extern const struct file_operations debugfs_full_proxy_file_operations;
|
|
|
|
struct debugfs_fsdata {
|
|
const struct file_operations *real_fops;
|
|
refcount_t active_users;
|
|
struct completion active_users_drained;
|
|
};
|
|
|
|
#endif /* _DEBUGFS_INTERNAL_H_ */
|