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Robin Murphy bfb9e836cf perf/arm-cci: Remove broken race mitigation [ Upstream commit `0d2e2a82d4` ] Uncore PMU drivers face an awkward cyclic dependency wherein: - They have to pick a valid online CPU to associate with before registering the PMU device, since it will get exposed to userspace immediately. - The PMU registration has to be be at least partly complete before hotplug events can be handled, since trying to migrate an uninitialised context would be bad. - The hotplug handler has to be ready as soon as a CPU is chosen, lest it go offline without the user-visible cpumask value getting updated. The arm-cci driver has tried to solve this by using get_cpu() to pick the current CPU and prevent it from disappearing while both registrations are performed, but that results in taking mutexes with preemption disabled, which makes certain configurations very unhappy: [ 1.983337] BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:2004 [ 1.983340] in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: swapper/0 [ 1.983342] Preemption disabled at: [ 1.983353] [<ffffff80089801f4>] cci_pmu_probe+0x1dc/0x488 [ 1.983360] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.20-rt8-yocto-preempt-rt #1 [ 1.983362] Hardware name: ZynqMP ZCU102 Rev1.0 (DT) [ 1.983364] Call trace: [ 1.983369] dump_backtrace+0x0/0x158 [ 1.983372] show_stack+0x24/0x30 [ 1.983378] dump_stack+0x80/0xa4 [ 1.983383] ___might_sleep+0x138/0x160 [ 1.983386] __might_sleep+0x58/0x90 [ 1.983391] __rt_mutex_lock_state+0x30/0xc0 [ 1.983395] _mutex_lock+0x24/0x30 [ 1.983400] perf_pmu_register+0x2c/0x388 [ 1.983404] cci_pmu_probe+0x2bc/0x488 [ 1.983409] platform_drv_probe+0x58/0xa8 It is not feasible to resolve all the possible races outside of the perf core itself, so address the immediate bug by following the example of nearly every other PMU driver and not even trying to do so. Registering the hotplug notifier first should minimise the window in which things can go wrong, so that's about as much as we can reasonably do here. This also revealed an additional race in assigning the global pointer too late relative to the hotplug notifier, which gets fixed in the process. Reported-by: Li, Meng <Meng.Li@windriver.com> Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com> Signed-off-by: Robin Murphy <robin.murphy@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Sasha Levin <sashal@kernel.org>		2019-05-31 06:46:17 -07:00
arch	x86/mm: Remove in_nmi() warning from 64-bit implementation of vmalloc_fault()	2019-05-31 06:46:16 -07:00
block	bfq: update internal depth state when queue depth changes	2019-05-16 19:41:17 +02:00
certs	export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR()	2018-08-22 23:21:44 +09:00
crypto	crypto: ccm - fix incompatibility between "ccm" and "ccm_base"	2019-05-22 07:37:43 +02:00
Documentation	arm64: errata: Add workaround for Cortex-A76 erratum #1463225	2019-05-31 06:46:03 -07:00
drivers	perf/arm-cci: Remove broken race mitigation	2019-05-31 06:46:17 -07:00
firmware	kbuild: remove all dummy assignments to obj-	2017-11-18 11:46:06 +09:00
fs	btrfs: Don't panic when we can't find a root key	2019-05-31 06:46:13 -07:00
include	smpboot: Place the __percpu annotation correctly	2019-05-31 06:46:16 -07:00
init	init: initialize jump labels before command line option parsing	2019-05-16 19:41:23 +02:00
ipc	ipc/shm.c: use ERR_CAST() for shm_lock() error return	2018-10-05 16:32:04 -07:00
kernel	sched/nohz: Run NOHZ idle load balancer on HK_FLAG_MISC CPUs	2019-05-31 06:46:14 -07:00
lib	mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions	2019-05-31 06:46:16 -07:00
LICENSES	LICENSES: Remove CC-BY-SA-4.0 license text	2018-10-18 11:28:50 +02:00
mm	hugetlb: use same fault hash key for shared and private mappings	2019-05-22 07:37:40 +02:00
net	mac80211/cfg80211: update bss channel on channel switch	2019-05-31 06:46:14 -07:00
samples	samples: mei: use /dev/mei0 instead of /dev/mei	2019-02-15 08:10:11 +01:00
scripts	fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock	2019-05-08 07:21:51 +02:00
security	apparmorfs: fix use-after-free on symlink traversal	2019-05-25 18:23:42 +02:00
sound	ASoC: fsl_sai: Update is_slave_mode with correct value	2019-05-31 06:46:14 -07:00
tools	libbpf: fix samples/bpf build failure due to undefined UINT32_MAX	2019-05-31 06:46:14 -07:00
usr	initramfs: move gen_initramfs_list.sh from scripts/ to usr/	2018-08-22 23:21:44 +09:00
virt	KVM: arm/arm64: Ensure vcpu target is unset on reset failure	2019-05-25 18:23:44 +02:00
.clang-format	clang-format: Set IndentWrappedFunctionNames false	2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore	Kbuild updates for v4.17 (2nd)	2018-04-15 17:21:30 -07:00
.mailmap	libnvdimm-for-4.19_misc	2018-08-25 18:13:10 -07:00
COPYING	COPYING: use the new text with points to the license files	2018-03-23 12:41:45 -06:00
CREDITS	9p: remove Ron Minnich from MAINTAINERS	2018-08-17 16:20:26 -07:00
Kbuild	Kbuild updates for v4.15	2017-11-17 17:45:29 -08:00
Kconfig	kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt	2018-08-02 08:06:55 +09:00
MAINTAINERS	platform/x86: Add Intel AtomISP2 dummy / power-management driver	2019-04-20 09:16:02 +02:00
Makefile	Linux 4.19.46	2019-05-25 18:23:48 +02:00
README	Docs: Added a pointer to the formatted docs to README	2018-03-21 09:02:53 -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.
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.