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Matt Redfearn 9e8c399a88 MIPS: SMP: Fix deadlock & online race 
Commit 6f542ebeae ("MIPS: Fix race on setting and getting
cpu_online_mask") effectively reverted commit 8f46cca1e6 ("MIPS: SMP:
Fix possibility of deadlock when bringing CPUs online") and thus has
reinstated the possibility of deadlock.

The commit was based on testing of kernel v4.4, where the CPU hotplug
core code issued a BUG() if the starting CPU is not marked online when
the boot CPU returns from __cpu_up. The commit fixes this race (in
v4.4), but re-introduces the deadlock situation.

As noted in the commit message, upstream differs in this area. Commit
8df3e07e7f ("cpu/hotplug: Let upcoming cpu bring itself fully up")
adds a completion event in the CPU hotplug core code, making this race
impossible. However, people were unhappy with relying on the core code
to do the right thing.

To address the issues both commits were trying to fix, add a second
completion event in the MIPS smp hotplug path. It removes the
possibility of a race, since the MIPS smp hotplug code now synchronises
both the boot and secondary CPUs before they return to the hotplug core
code. It also addresses the deadlock by ensuring that the secondary CPU
is not marked online before it's counters are synchronised.

This fix should also be backported to fix the race condition introduced
by the backport of commit 8f46cca1e6 ("MIPS: SMP: Fix possibility of
deadlock when bringing CPUs online"), through really that race only
existed before commit 8df3e07e7f ("cpu/hotplug: Let upcoming cpu
bring itself fully up").

Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Fixes: 6f542ebeae ("MIPS: Fix race on setting and getting cpu_online_mask")
CC: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@nokia.com>
Cc: <stable@vger.kernel.org> # v4.1+: 8f46cca1e6: "MIPS: SMP: Fix possibility of deadlock when bringing CPUs online"
Cc: <stable@vger.kernel.org> # v4.1+: a00eeede50: "MIPS: SMP: Use a completion event to signal CPU up"
Cc: <stable@vger.kernel.org> # v4.1+: 6f542ebeae: "MIPS: Fix race on setting and getting cpu_online_mask"
Cc: <stable@vger.kernel.org> # v4.1+
Patchwork: https://patchwork.linux-mips.org/patch/17376/
Signed-off-by: James Hogan <jhogan@kernel.org>
2017-11-01 00:09:17 +00:00
arch MIPS: SMP: Fix deadlock & online race 2017-11-01 00:09:17 +00:00
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 Merge commit 'tags/keys-fixes-20171018' into fixes-v4.14-rc5 2017-10-19 12:28:38 +11:00
Documentation Update MIPS email addresses 2017-10-31 22:42:39 +00:00
drivers Update MIPS email addresses 2017-10-31 22:42:39 +00:00
firmware firmware: Restore support for built-in firmware 2017-09-16 10:58:48 -07:00
fs Various SMB3 fixes for 4.14 and stable 2017-10-28 08:39:35 -07:00
include Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-10-29 08:11:49 -07:00
init kbuild: Fix optimization level choice default 2017-10-07 20:08:05 +09:00
ipc fix a typo in put_compat_shm_info() 2017-09-25 20:41:46 -04:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-10-29 08:11:49 -07:00
lib assoc_array: Fix a buggy node-splitting case 2017-10-28 10:31:07 -07:00
mm Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-10-21 22:44:48 -04:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-10-29 08:11:49 -07:00
samples Fix tracing sample code warning. 2017-10-27 20:35:31 -07:00
scripts Kbuild fixes for v4.14 (2nd) 2017-10-28 11:01:57 -07:00
security Revert "apparmor: add base infastructure for socket mediation" 2017-10-26 19:35:35 +02:00
sound ALSA: hda - fix headset mic problem for Dell machines with alc236 2017-10-24 14:32:24 +02:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-10-29 08:11:49 -07:00
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 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: Add support to generate LLVM assembly files 2017-04-25 08:13:52 +09:00
.mailmap Update MIPS email addresses 2017-10-31 22:42:39 +00:00
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 Update MIPS email addresses 2017-10-31 22:42:39 +00:00
Makefile Linux 4.14-rc7 2017-10-29 13:58:38 -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.