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Nicolai Stange e9117a5a4b debugfs: implement per-file removal protection 
Since commit 49d200deaa ("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>
2017-11-07 20:25:02 +01:00
arch Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-10-14 15:26:38 -04:00
block bio_copy_user_iov(): don't ignore ->iov_offset 2017-10-10 23:55:14 -04:00
certs modsign: add markers to endif-statements in certs/Makefile 2017-07-14 11:01:37 +10:00
crypto crypto: shash - Fix zero-length shash ahash digest crash 2017-10-11 00:34:07 +08:00
Documentation mm, swap: use page-cluster as max window of VMA based swap readahead 2017-10-13 16:18:33 -07:00
drivers driver core: Move device_links_purge() after bus_remove_device() 2017-10-20 16:33:13 +02:00
firmware firmware: Restore support for built-in firmware 2017-09-16 10:58:48 -07:00
fs debugfs: implement per-file removal protection 2017-11-07 20:25:02 +01:00
include debugfs: implement per-file removal protection 2017-11-07 20:25:02 +01:00
init Merge branch 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-09-14 18:54:01 -07:00
ipc fix a typo in put_compat_shm_info() 2017-09-25 20:41:46 -04:00
kernel Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-10-14 15:20:38 -04:00
lib Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-10-14 15:14:20 -04:00
mm mm, swap: use page-cluster as max window of VMA based swap readahead 2017-10-13 16:18:33 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-10-09 16:25:00 -07:00
samples media updates for v4.14-rc1 2017-09-07 12:53:14 -07:00
scripts scripts/kallsyms.c: ignore symbol type 'n' 2017-10-13 16:18:32 -07:00
security lsm: fix smack_inode_removexattr and xattr_getsecurity memleak 2017-10-04 18:03:15 +11:00
sound ALSA: caiaq: Fix stray URB at probe error path 2017-10-11 17:01:18 +02:00
tools Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-10-14 15:16:49 -04:00
usr ramfs: clarify help text that compression applies to ramfs as well as legacy ramdisk. 2017-07-06 16:24:30 -07:00
virt Revert "KVM: Don't accept obviously wrong gsi values via KVM_IRQFD" 2017-09-19 08:37:17 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support to generate LLVM assembly files 2017-04-25 08:13:52 +09:00
.mailmap Update James Hogan's email address 2017-10-04 17:11:53 -07:00
COPYING
CREDITS selinux/stable-4.14 PR 20170831 2017-09-12 13:21:00 -07:00
Kbuild kbuild: Consolidate header generation from ASM offset information 2017-04-13 05:43:37 +09:00
Kconfig
MAINTAINERS Another latent bug related to PCID, an out-of-bounds access, 2017-10-12 10:42:03 -07:00
Makefile Linux 4.14-rc5 2017-10-15 21:01:12 -04:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.