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Jean-Philippe Brucker 682d3a98ab mm/mmu_notifier: use hlist_add_head_rcu() 
[ Upstream commit 543bdb2d82 ]

Make mmu_notifier_register() safer by issuing a memory barrier before
registering a new notifier.  This fixes a theoretical bug on weakly
ordered CPUs.  For example, take this simplified use of notifiers by a
driver:

	my_struct->mn.ops = &my_ops; /* (1) */
	mmu_notifier_register(&my_struct->mn, mm)
		...
		hlist_add_head(&mn->hlist, &mm->mmu_notifiers); /* (2) */
		...

Once mmu_notifier_register() releases the mm locks, another thread can
invalidate a range:

	mmu_notifier_invalidate_range()
		...
		hlist_for_each_entry_rcu(mn, &mm->mmu_notifiers, hlist) {
			if (mn->ops->invalidate_range)

The read side relies on the data dependency between mn and ops to ensure
that the pointer is properly initialized.  But the write side doesn't have
any dependency between (1) and (2), so they could be reordered and the
readers could dereference an invalid mn->ops.  mmu_notifier_register()
does take all the mm locks before adding to the hlist, but those have
acquire semantics which isn't sufficient.

By calling hlist_add_head_rcu() instead of hlist_add_head() we update the
hlist using a store-release, ensuring that readers see prior
initialization of my_struct.  This situation is better illustated by
litmus test MP+onceassign+derefonce.

Link: http://lkml.kernel.org/r/20190502133532.24981-1-jean-philippe.brucker@arm.com
Fixes: cddb8a5c14 ("mmu-notifiers: core")
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2019-07-31 07:28:56 +02:00
arch sh: prevent warnings when using iounmap 2019-07-31 07:28:55 +02:00
block block/bio-integrity: fix a memory leak bug 2019-07-31 07:28:55 +02:00
certs Replace magic for trusting the secondary keyring with #define 2018-09-09 19:55:54 +02:00
crypto crypto: chacha20poly1305 - fix atomic sleep when using async algorithm 2019-07-31 07:28:35 +02:00
Documentation dt-bindings: allow up to four clocks for orion-mdio 2019-07-31 07:28:43 +02:00
drivers mailbox: handle failed named mailbox channel request 2019-07-31 07:28:55 +02:00
firmware License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fs 9p: pass the correct prototype to read_cache_page 2019-07-31 07:28:55 +02:00
include jbd2: introduce jbd2_inode dirty range scoping 2019-07-31 07:28:47 +02:00
init init: initialize jump labels before command line option parsing 2019-05-16 19:42:23 +02:00
ipc ipc: prevent lockup on alloc_msg and free_msg 2019-06-15 11:54:51 +02:00
kernel padata: use smp_mb in padata_reorder to avoid orphaned padata jobs 2019-07-31 07:28:39 +02:00
lib lib/strscpy: Shut up KASAN false-positives in strscpy() 2019-07-31 07:28:44 +02:00
mm mm/mmu_notifier: use hlist_add_head_rcu() 2019-07-31 07:28:56 +02:00
net hvsock: fix epollout hang from race condition 2019-07-31 07:28:48 +02:00
samples samples, bpf: fix to change the buffer size for read() 2019-07-21 09:04:17 +02:00
scripts kallsyms: exclude kasan local symbols on s390 2019-07-31 07:28:54 +02:00
security apparmor: enforce nullbyte at end of tag string 2019-06-25 11:36:51 +08:00
sound ALSA: hda/realtek: apply ALC891 headset fixup to one Dell machine 2019-07-31 07:28:38 +02:00
tools perf annotate: Fix dereferencing freed memory found by the smatch tool 2019-07-31 07:28:54 +02:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM: arm/arm64: vgic: Fix kvm_device leak in vgic_its_destroy 2019-07-21 09:04:24 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS MAINTAINERS: Add Sasha as a stable branch maintainer 2018-12-01 09:42:50 +01:00
Makefile kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS 2019-07-31 07:28:52 +02:00
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.