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Gaurav Kohli cb71229f64 timers: Clear timer_base::must_forward_clk with timer_base::lock held 
[ Upstream commit 363e934d88 ]

timer_base::must_forward_clock is indicating that the base clock might be
stale due to a long idle sleep.

The forwarding of the base clock takes place in the timer softirq or when a
timer is enqueued to a base which is idle. If the enqueue of timer to an
idle base happens from a remote CPU, then the following race can happen:

  CPU0					CPU1
  run_timer_softirq			mod_timer

					base = lock_timer_base(timer);
  base->must_forward_clk = false
					if (base->must_forward_clk)
				       	    forward(base); -> skipped

					enqueue_timer(base, timer, idx);
					-> idx is calculated high due to
					   stale base
					unlock_timer_base(timer);
  base = lock_timer_base(timer);
  forward(base);

The root cause is that timer_base::must_forward_clk is cleared outside the
timer_base::lock held region, so the remote queuing CPU observes it as
cleared, but the base clock is still stale. This can cause large
granularity values for timers, i.e. the accuracy of the expiry time
suffers.

Prevent this by clearing the flag with timer_base::lock held, so that the
forwarding takes place before the cleared flag is observable by a remote
CPU.

Signed-off-by: Gaurav Kohli <gkohli@codeaurora.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: john.stultz@linaro.org
Cc: sboyd@kernel.org
Cc: linux-arm-msm@vger.kernel.org
Link: https://lkml.kernel.org/r/1533199863-22748-1-git-send-email-gkohli@codeaurora.org
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2018-09-19 22:43:39 +02:00
Documentation kbuild: verify that $DEPMOD is installed 2018-08-17 21:01:10 +02:00
arch powerpc/powernv: Fix concurrency issue with npu->mmio_atsd_usage 2018-09-19 22:43:38 +02:00
block blk-mq: fix updating tags depth 2018-09-19 22:43:39 +02:00
certs Replace magic for trusting the secondary keyring with #define 2018-09-09 19:55:54 +02:00
crypto crypto: aes-generic - fix aes-generic regression on powerpc 2018-09-19 22:43:37 +02:00
drivers md/raid5: fix data corruption of replacements after originals dropped 2018-09-19 22:43:39 +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 Btrfs: fix data corruption when deduplicating between different files 2018-09-19 22:43:36 +02:00
include ethtool: Remove trailing semicolon for static inline 2018-09-19 22:43:38 +02:00
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 timers: Clear timer_base::must_forward_clk with timer_base::lock held 2018-09-19 22:43:39 +02:00
lib debugobjects: Make stack check warning more informative 2018-09-15 09:45:35 +02:00
mm mm/fadvise.c: fix signed overflow UBSAN complaint 2018-09-15 09:45:28 +02:00
net RDS: IB: fix 'passing zero to ERR_PTR()' warning 2018-09-15 09:45:31 +02:00
samples samples/bpf: Check the error of write() and read() 2018-08-24 13:09:12 +02:00
scripts kbuild: make missing $DEPMOD a Warning instead of an Error 2018-09-15 09:45:36 +02:00
security uapi/linux/keyctl.h: don't use C++ reserved keyword as a struct member name 2018-09-15 09:45:35 +02:00
sound ALSA: hda - Fix cancel_work_sync() stall from jackpoll work 2018-09-19 22:43:36 +02:00
tools selftests/bpf: fix a typo in map in map test 2018-09-19 22:43:38 +02:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM: arm/arm64: Skip updating PTE entry if no change 2018-09-05 09:26:36 +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 4.14.70 2018-09-15 09:45:37 +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.