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Alan Stern dde38b5cf1 tools/memory-model: Fix data race detection for unordered store and load 
[ Upstream commit daebf24a8e ]

Currently the Linux Kernel Memory Model gives an incorrect response
for the following litmus test:

C plain-WWC

{}

P0(int *x)
{
	WRITE_ONCE(*x, 2);
}

P1(int *x, int *y)
{
	int r1;
	int r2;
	int r3;

	r1 = READ_ONCE(*x);
	if (r1 == 2) {
		smp_rmb();
		r2 = *x;
	}
	smp_rmb();
	r3 = READ_ONCE(*x);
	WRITE_ONCE(*y, r3 - 1);
}

P2(int *x, int *y)
{
	int r4;

	r4 = READ_ONCE(*y);
	if (r4 > 0)
		WRITE_ONCE(*x, 1);
}

exists (x=2 /\ 1:r2=2 /\ 2:r4=1)

The memory model says that the plain read of *x in P1 races with the
WRITE_ONCE(*x) in P2.

The problem is that we have a write W and a read R related by neither
fre or rfe, but rather W ->coe W' ->rfe R, where W' is an intermediate
write (the WRITE_ONCE() in P0).  In this situation there is no
particular ordering between W and R, so either a wr-vis link from W to
R or an rw-xbstar link from R to W would prove that the accesses
aren't concurrent.

But the LKMM only looks for a wr-vis link, which is equivalent to
assuming that W must execute before R.  This is not necessarily true
on non-multicopy-atomic systems, as the WWC pattern demonstrates.

This patch changes the LKMM to accept either a wr-vis or a reverse
rw-xbstar link as a proof of non-concurrency.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2019-12-31 16:43:40 +01:00
Documentation USB: documentation: flags on usb-storage versus UAS 2019-12-17 19:55:32 +01:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch x86/math-emu: Check __copy_from_user() result 2019-12-31 16:43:32 +01:00
block block: fix "check bi_size overflow before merge" 2019-12-21 11:04:32 +01:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: aegis128-neon - use Clang compatible cflags for ARM 2019-12-31 16:43:38 +01:00
drivers regulator: max8907: Fix the usage of uninitialized variable in max8907_regulator_probe() 2019-12-31 16:43:39 +01:00
fs Btrfs: fix removal logic of the tree mod log that leads to use-after-free issues 2019-12-31 16:42:07 +01:00
include drm: mst: Fix query_payload ack reply struct 2019-12-31 16:42:19 +01:00
init Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
ipc ipc/sem.c: convert to use built-in RCU list checking 2019-09-25 17:51:41 -07:00
kernel workqueue: Fix missing kfree(rescuer) in destroy_workqueue() 2019-12-17 19:56:54 +01:00
lib lib: raid6: fix awk build warnings 2019-12-17 19:56:09 +01:00
mm mm/shmem.c: cast the type of unmap_start to u64 2019-12-17 19:56:51 +01:00
net neighbour: remove neigh_cleanup() method 2019-12-31 16:41:37 +01:00
samples samples/bpf: fix build by setting HAVE_ATTR_TEST to zero 2019-10-31 21:39:15 +01:00
scripts arm64 fix for -rc8 / final 2019-11-15 09:14:23 -08:00
security efi/efi_test: Lock down /dev/efi_test and require CAP_SYS_ADMIN 2019-10-31 09:40:21 +01:00
sound ALSA: hda/ca0132 - Fix work handling in delayed HP detection 2019-12-31 16:42:12 +01:00
tools tools/memory-model: Fix data race detection for unordered store and load 2019-12-31 16:43:40 +01:00
usr kbuild: update compile-test header list for v5.4-rc2 2019-10-05 15:29:49 +09:00
virt KVM: arm/arm64: vgic: Don't rely on the wrong pending table 2019-12-13 08:43:00 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-11-22 14:28:14 -08:00
Makefile Linux 5.4.6 2019-12-21 11:05:23 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

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.