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Olaf Hering a502165dae xen: avoid crash in disable_hotplug_cpu 
[ Upstream commit 3366cdb6d3 ]

The command 'xl vcpu-set 0 0', issued in dom0, will crash dom0:

BUG: unable to handle kernel NULL pointer dereference at 00000000000002d8
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP NOPTI
CPU: 7 PID: 65 Comm: xenwatch Not tainted 4.19.0-rc2-1.ga9462db-default #1 openSUSE Tumbleweed (unreleased)
Hardware name: Intel Corporation S5520UR/S5520UR, BIOS S5500.86B.01.00.0050.050620101605 05/06/2010
RIP: e030:device_offline+0x9/0xb0
Code: 77 24 00 e9 ce fe ff ff 48 8b 13 e9 68 ff ff ff 48 8b 13 e9 29 ff ff ff 48 8b 13 e9 ea fe ff ff 90 66 66 66 66 90 41 54 55 53 <f6> 87 d8 02 00 00 01 0f 85 88 00 00 00 48 c7 c2 20 09 60 81 31 f6
RSP: e02b:ffffc90040f27e80 EFLAGS: 00010203
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff8801f3800000 RSI: ffffc90040f27e70 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff820e47b3 R09: 0000000000000000
R10: 0000000000007ff0 R11: 0000000000000000 R12: ffffffff822e6d30
R13: dead000000000200 R14: dead000000000100 R15: ffffffff8158b4e0
FS:  00007ffa595158c0(0000) GS:ffff8801f39c0000(0000) knlGS:0000000000000000
CS:  e033 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000002d8 CR3: 00000001d9602000 CR4: 0000000000002660
Call Trace:
 handle_vcpu_hotplug_event+0xb5/0xc0
 xenwatch_thread+0x80/0x140
 ? wait_woken+0x80/0x80
 kthread+0x112/0x130
 ? kthread_create_worker_on_cpu+0x40/0x40
 ret_from_fork+0x3a/0x50

This happens because handle_vcpu_hotplug_event is called twice. In the
first iteration cpu_present is still true, in the second iteration
cpu_present is false which causes get_cpu_device to return NULL.
In case of cpu#0, cpu_online is apparently always true.

Fix this crash by checking if the cpu can be hotplugged, which is false
for a cpu that was just removed.

Also check if the cpu was actually offlined by device_remove, otherwise
leave the cpu_present state as it is.

Rearrange to code to do all work with device_hotplug_lock held.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2018-10-10 08:54:26 +02:00
Documentation hwmon: (ina2xx) fix sysfs shunt resistor read access 2018-10-03 17:00:58 -07:00
arch arm64: jump_label.h: use asm_volatile_goto macro instead of "asm goto" 2018-10-10 08:54:25 +02:00
block blk-mq: avoid to synchronize rcu inside blk_cleanup_queue() 2018-09-26 08:38:13 +02:00
certs Replace magic for trusting the secondary keyring with #define 2018-09-09 19:55:54 +02:00
crypto crypto: skcipher - Fix -Wstringop-truncation warnings 2018-10-03 17:00:45 -07:00
drivers xen: avoid crash in disable_hotplug_cpu 2018-10-10 08:54:26 +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 cifs: read overflow in is_valid_oplock_break() 2018-10-10 08:54:26 +02:00
include media: v4l: event: Prevent freeing event subscriptions while accessed 2018-10-03 17:01:00 -07:00
init init: rename and re-order boot_cpu_state_init() 2018-08-15 18:12:48 +02:00
ipc ipc/sem.c: prevent queue.status tearing in semop 2018-09-05 09:26:30 +02:00
kernel bpf: 32-bit RSH verification must truncate input before the ALU op 2018-10-10 08:54:22 +02:00
lib scsi: klist: Make it safe to use klists in atomic context 2018-10-03 17:00:48 -07:00
mm mm: madvise(MADV_DODUMP): allow hugetlbfs pages 2018-10-10 08:54:22 +02:00
net netfilter: nf_tables: release chain in flushing set 2018-10-10 08:54:23 +02:00
samples samples/bpf: Check the error of write() and read() 2018-08-24 13:09:12 +02:00
scripts kbuild: add .DELETE_ON_ERROR special target 2018-09-26 08:37:59 +02:00
security Revert "uapi/linux/keyctl.h: don't use C++ reserved keyword as a struct member name" 2018-09-29 03:06:04 -07:00
sound ASoC: dapm: Fix potential DAI widget pointer deref when linking DAIs 2018-10-03 17:00:53 -07:00
tools perf probe powerpc: Ignore SyS symbols irrespective of endianness 2018-10-10 08:54:23 +02:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM: arm/arm64: Fix vgic init race 2018-09-26 08:38:04 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.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 dt-bindings: Document mti,mips-cpc binding 2018-03-15 10:54:35 +01:00
Makefile Linux 4.14.74 2018-10-03 17:01:00 -07:00
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.