Revision 63cae12bce9861cec309798d34701cf3da20bc71 authored by Peter Zijlstra on 09 December 2016, 13:59:00 UTC, committed by Ingo Molnar on 14 January 2017, 09:56:10 UTC
There is problem with installing an event in a task that is 'stuck' on
an offline CPU.
Blocked tasks are not dis-assosciated from offlined CPUs, after all, a
blocked task doesn't run and doesn't require a CPU etc.. Only on
wakeup do we ammend the situation and place the task on a available
CPU.
If we hit such a task with perf_install_in_context() we'll loop until
either that task wakes up or the CPU comes back online, if the task
waking depends on the event being installed, we're stuck.
While looking into this issue, I also spotted another problem, if we
hit a task with perf_install_in_context() that is in the middle of
being migrated, that is we observe the old CPU before sending the IPI,
but run the IPI (on the old CPU) while the task is already running on
the new CPU, things also go sideways.
Rework things to rely on task_curr() -- outside of rq->lock -- which
is rather tricky. Imagine the following scenario where we're trying to
install the first event into our task 't':
CPU0 CPU1 CPU2
(current == t)
t->perf_event_ctxp[] = ctx;
smp_mb();
cpu = task_cpu(t);
switch(t, n);
migrate(t, 2);
switch(p, t);
ctx = t->perf_event_ctxp[]; // must not be NULL
smp_function_call(cpu, ..);
generic_exec_single()
func();
spin_lock(ctx->lock);
if (task_curr(t)) // false
add_event_to_ctx();
spin_unlock(ctx->lock);
perf_event_context_sched_in();
spin_lock(ctx->lock);
// sees event
So its CPU0's store of t->perf_event_ctxp[] that must not go 'missing'.
Because if CPU2's load of that variable were to observe NULL, it would
not try to schedule the ctx and we'd have a task running without its
counter, which would be 'bad'.
As long as we observe !NULL, we'll acquire ctx->lock. If we acquire it
first and not see the event yet, then CPU0 must observe task_curr()
and retry. If the install happens first, then we must see the event on
sched-in and all is well.
I think we can translate the first part (until the 'must not be NULL')
of the scenario to a litmus test like:
C C-peterz
{
}
P0(int *x, int *y)
{
int r1;
WRITE_ONCE(*x, 1);
smp_mb();
r1 = READ_ONCE(*y);
}
P1(int *y, int *z)
{
WRITE_ONCE(*y, 1);
smp_store_release(z, 1);
}
P2(int *x, int *z)
{
int r1;
int r2;
r1 = smp_load_acquire(z);
smp_mb();
r2 = READ_ONCE(*x);
}
exists
(0:r1=0 /\ 2:r1=1 /\ 2:r2=0)
Where:
x is perf_event_ctxp[],
y is our tasks's CPU, and
z is our task being placed on the rq of CPU2.
The P0 smp_mb() is the one added by this patch, ordering the store to
perf_event_ctxp[] from find_get_context() and the load of task_cpu()
in task_function_call().
The smp_store_release/smp_load_acquire model the RCpc locking of the
rq->lock and the smp_mb() of P2 is the context switch switching from
whatever CPU2 was running to our task 't'.
This litmus test evaluates into:
Test C-peterz Allowed
States 7
0:r1=0; 2:r1=0; 2:r2=0;
0:r1=0; 2:r1=0; 2:r2=1;
0:r1=0; 2:r1=1; 2:r2=1;
0:r1=1; 2:r1=0; 2:r2=0;
0:r1=1; 2:r1=0; 2:r2=1;
0:r1=1; 2:r1=1; 2:r2=0;
0:r1=1; 2:r1=1; 2:r2=1;
No
Witnesses
Positive: 0 Negative: 7
Condition exists (0:r1=0 /\ 2:r1=1 /\ 2:r2=0)
Observation C-peterz Never 0 7
Hash=e427f41d9146b2a5445101d3e2fcaa34
And the strong and weak model agree.
Reported-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Will Deacon <will.deacon@arm.com>
Cc: jeremy.linton@arm.com
Link: http://lkml.kernel.org/r/20161209135900.GU3174@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 parent ad5013d
Kconfig
menuconfig PWM
bool "Pulse-Width Modulation (PWM) Support"
help
Generic Pulse-Width Modulation (PWM) support.
In Pulse-Width Modulation, a variation of the width of pulses
in a rectangular pulse signal is used as a means to alter the
average power of the signal. Applications include efficient
power delivery and voltage regulation. In computer systems,
PWMs are commonly used to control fans or the brightness of
display backlights.
This framework provides a generic interface to PWM devices
within the Linux kernel. On the driver side it provides an API
to register and unregister a PWM chip, an abstraction of a PWM
controller, that supports one or more PWM devices. Client
drivers can request PWM devices and use the generic framework
to configure as well as enable and disable them.
This generic framework replaces the legacy PWM framework which
allows only a single driver implementing the required API. Not
all legacy implementations have been ported to the framework
yet. The framework provides an API that is backward compatible
with the legacy framework so that existing client drivers
continue to work as expected.
If unsure, say no.
if PWM
config PWM_SYSFS
bool
default y if SYSFS
config PWM_AB8500
tristate "AB8500 PWM support"
depends on AB8500_CORE && ARCH_U8500
help
Generic PWM framework driver for Analog Baseband AB8500.
To compile this driver as a module, choose M here: the module
will be called pwm-ab8500.
config PWM_ATMEL
tristate "Atmel PWM support"
depends on ARCH_AT91 || AVR32
help
Generic PWM framework driver for Atmel SoC.
To compile this driver as a module, choose M here: the module
will be called pwm-atmel.
config PWM_ATMEL_HLCDC_PWM
tristate "Atmel HLCDC PWM support"
depends on MFD_ATMEL_HLCDC
depends on HAVE_CLK
help
Generic PWM framework driver for the PWM output of the HLCDC
(Atmel High-end LCD Controller). This PWM output is mainly used
to control the LCD backlight.
To compile this driver as a module, choose M here: the module
will be called pwm-atmel-hlcdc.
config PWM_ATMEL_TCB
tristate "Atmel TC Block PWM support"
depends on ATMEL_TCLIB && OF
help
Generic PWM framework driver for Atmel Timer Counter Block.
A Timer Counter Block provides 6 PWM devices grouped by 2.
Devices in a given group must have the same period.
To compile this driver as a module, choose M here: the module
will be called pwm-atmel-tcb.
config PWM_BCM_IPROC
tristate "iProc PWM support"
depends on ARCH_BCM_IPROC
help
Generic PWM framework driver for Broadcom iProc PWM block. This
block is used in Broadcom iProc SoC's.
To compile this driver as a module, choose M here: the module
will be called pwm-bcm-iproc.
config PWM_BCM_KONA
tristate "Kona PWM support"
depends on ARCH_BCM_MOBILE
help
Generic PWM framework driver for Broadcom Kona PWM block.
To compile this driver as a module, choose M here: the module
will be called pwm-bcm-kona.
config PWM_BCM2835
tristate "BCM2835 PWM support"
depends on ARCH_BCM2835
help
PWM framework driver for BCM2835 controller (Raspberry Pi)
To compile this driver as a module, choose M here: the module
will be called pwm-bcm2835.
config PWM_BERLIN
tristate "Marvell Berlin PWM support"
depends on ARCH_BERLIN
help
PWM framework driver for Marvell Berlin SoCs.
To compile this driver as a module, choose M here: the module
will be called pwm-berlin.
config PWM_BFIN
tristate "Blackfin PWM support"
depends on BFIN_GPTIMERS
help
Generic PWM framework driver for Blackfin.
To compile this driver as a module, choose M here: the module
will be called pwm-bfin.
config PWM_BRCMSTB
tristate "Broadcom STB PWM support"
depends on ARCH_BRCMSTB || BMIPS_GENERIC
help
Generic PWM framework driver for the Broadcom Set-top-Box
SoCs (BCM7xxx).
To compile this driver as a module, choose M Here: the module
will be called pwm-brcmstb.c.
config PWM_CLPS711X
tristate "CLPS711X PWM support"
depends on ARCH_CLPS711X || COMPILE_TEST
depends on HAS_IOMEM
help
Generic PWM framework driver for Cirrus Logic CLPS711X.
To compile this driver as a module, choose M here: the module
will be called pwm-clps711x.
config PWM_CRC
bool "Intel Crystalcove (CRC) PWM support"
depends on X86 && INTEL_SOC_PMIC
help
Generic PWM framework driver for Crystalcove (CRC) PMIC based PWM
control.
config PWM_CROS_EC
tristate "ChromeOS EC PWM driver"
depends on MFD_CROS_EC
help
PWM driver for exposing a PWM attached to the ChromeOS Embedded
Controller.
config PWM_EP93XX
tristate "Cirrus Logic EP93xx PWM support"
depends on ARCH_EP93XX
help
Generic PWM framework driver for Cirrus Logic EP93xx.
To compile this driver as a module, choose M here: the module
will be called pwm-ep93xx.
config PWM_FSL_FTM
tristate "Freescale FlexTimer Module (FTM) PWM support"
depends on HAS_IOMEM
depends on OF
select REGMAP_MMIO
help
Generic FTM PWM framework driver for Freescale VF610 and
Layerscape LS-1 SoCs.
To compile this driver as a module, choose M here: the module
will be called pwm-fsl-ftm.
config PWM_HIBVT
tristate "HiSilicon BVT PWM support"
depends on ARCH_HISI || COMPILE_TEST
help
Generic PWM framework driver for HiSilicon BVT SoCs.
To compile this driver as a module, choose M here: the module
will be called pwm-hibvt.
config PWM_IMG
tristate "Imagination Technologies PWM driver"
depends on HAS_IOMEM
depends on MFD_SYSCON
depends on COMMON_CLK
depends on MIPS || COMPILE_TEST
help
Generic PWM framework driver for Imagination Technologies
PWM block which supports 4 channels.
To compile this driver as a module, choose M here: the module
will be called pwm-img
config PWM_IMX
tristate "i.MX PWM support"
depends on ARCH_MXC
help
Generic PWM framework driver for i.MX.
To compile this driver as a module, choose M here: the module
will be called pwm-imx.
config PWM_JZ4740
tristate "Ingenic JZ4740 PWM support"
depends on MACH_JZ4740
help
Generic PWM framework driver for Ingenic JZ4740 based
machines.
To compile this driver as a module, choose M here: the module
will be called pwm-jz4740.
config PWM_LP3943
tristate "TI/National Semiconductor LP3943 PWM support"
depends on MFD_LP3943
help
Generic PWM framework driver for LP3943 which supports two PWM
channels.
To compile this driver as a module, choose M here: the module
will be called pwm-lp3943.
config PWM_LPC18XX_SCT
tristate "LPC18xx/43xx PWM/SCT support"
depends on ARCH_LPC18XX
help
Generic PWM framework driver for NXP LPC18xx PWM/SCT which
supports 16 channels.
A maximum of 15 channels can be requested simultaneously and
must have the same period.
To compile this driver as a module, choose M here: the module
will be called pwm-lpc18xx-sct.
config PWM_LPC32XX
tristate "LPC32XX PWM support"
depends on ARCH_LPC32XX
help
Generic PWM framework driver for LPC32XX. The LPC32XX SOC has two
PWM controllers.
To compile this driver as a module, choose M here: the module
will be called pwm-lpc32xx.
config PWM_LPSS
tristate
config PWM_LPSS_PCI
tristate "Intel LPSS PWM PCI driver"
depends on X86 && PCI
select PWM_LPSS
help
The PCI driver for Intel Low Power Subsystem PWM controller.
To compile this driver as a module, choose M here: the module
will be called pwm-lpss-pci.
config PWM_LPSS_PLATFORM
tristate "Intel LPSS PWM platform driver"
depends on X86 && ACPI
select PWM_LPSS
help
The platform driver for Intel Low Power Subsystem PWM controller.
To compile this driver as a module, choose M here: the module
will be called pwm-lpss-platform.
config PWM_MESON
tristate "Amlogic Meson PWM driver"
depends on ARCH_MESON
help
The platform driver for Amlogic Meson PWM controller.
To compile this driver as a module, choose M here: the module
will be called pwm-meson.
config PWM_MTK_DISP
tristate "MediaTek display PWM driver"
depends on ARCH_MEDIATEK || COMPILE_TEST
depends on HAS_IOMEM
help
Generic PWM framework driver for MediaTek disp-pwm device.
The PWM is used to control the backlight brightness for display.
To compile this driver as a module, choose M here: the module
will be called pwm-mtk-disp.
config PWM_MXS
tristate "Freescale MXS PWM support"
depends on ARCH_MXS && OF
select STMP_DEVICE
help
Generic PWM framework driver for Freescale MXS.
To compile this driver as a module, choose M here: the module
will be called pwm-mxs.
config PWM_OMAP_DMTIMER
tristate "OMAP Dual-Mode Timer PWM support"
depends on OF && ARCH_OMAP && OMAP_DM_TIMER
help
Generic PWM framework driver for OMAP Dual-Mode Timer PWM output
To compile this driver as a module, choose M here: the module
will be called pwm-omap-dmtimer
config PWM_PCA9685
tristate "NXP PCA9685 PWM driver"
depends on I2C
select REGMAP_I2C
help
Generic PWM framework driver for NXP PCA9685 LED controller.
To compile this driver as a module, choose M here: the module
will be called pwm-pca9685.
config PWM_PUV3
tristate "PKUnity NetBook-0916 PWM support"
depends on ARCH_PUV3
help
Generic PWM framework driver for PKUnity NetBook-0916.
To compile this driver as a module, choose M here: the module
will be called pwm-puv3.
config PWM_PXA
tristate "PXA PWM support"
depends on ARCH_PXA
help
Generic PWM framework driver for PXA.
To compile this driver as a module, choose M here: the module
will be called pwm-pxa.
config PWM_RCAR
tristate "Renesas R-Car PWM support"
depends on ARCH_RENESAS || COMPILE_TEST
depends on HAS_IOMEM
help
This driver exposes the PWM Timer controller found in Renesas
R-Car chips through the PWM API.
To compile this driver as a module, choose M here: the module
will be called pwm-rcar.
config PWM_RENESAS_TPU
tristate "Renesas TPU PWM support"
depends on ARCH_RENESAS || COMPILE_TEST
depends on HAS_IOMEM
help
This driver exposes the Timer Pulse Unit (TPU) PWM controller found
in Renesas chips through the PWM API.
To compile this driver as a module, choose M here: the module
will be called pwm-renesas-tpu.
config PWM_ROCKCHIP
tristate "Rockchip PWM support"
depends on ARCH_ROCKCHIP
help
Generic PWM framework driver for the PWM controller found on
Rockchip SoCs.
config PWM_SAMSUNG
tristate "Samsung PWM support"
depends on PLAT_SAMSUNG || ARCH_EXYNOS
help
Generic PWM framework driver for Samsung.
To compile this driver as a module, choose M here: the module
will be called pwm-samsung.
config PWM_SPEAR
tristate "STMicroelectronics SPEAr PWM support"
depends on PLAT_SPEAR
depends on OF
help
Generic PWM framework driver for the PWM controller on ST
SPEAr SoCs.
To compile this driver as a module, choose M here: the module
will be called pwm-spear.
config PWM_STI
tristate "STiH4xx PWM support"
depends on ARCH_STI
depends on OF
help
Generic PWM framework driver for STiH4xx SoCs.
To compile this driver as a module, choose M here: the module
will be called pwm-sti.
config PWM_STMPE
bool "STMPE expander PWM export"
depends on MFD_STMPE
help
This enables support for the PWMs found in the STMPE I/O
expanders.
config PWM_SUN4I
tristate "Allwinner PWM support"
depends on ARCH_SUNXI || COMPILE_TEST
depends on HAS_IOMEM && COMMON_CLK
help
Generic PWM framework driver for Allwinner SoCs.
To compile this driver as a module, choose M here: the module
will be called pwm-sun4i.
config PWM_TEGRA
tristate "NVIDIA Tegra PWM support"
depends on ARCH_TEGRA
help
Generic PWM framework driver for the PWFM controller found on NVIDIA
Tegra SoCs.
To compile this driver as a module, choose M here: the module
will be called pwm-tegra.
config PWM_TIECAP
tristate "ECAP PWM support"
depends on ARCH_OMAP2PLUS || ARCH_DAVINCI_DA8XX
help
PWM driver support for the ECAP APWM controller found on AM33XX
TI SOC
To compile this driver as a module, choose M here: the module
will be called pwm-tiecap.
config PWM_TIEHRPWM
tristate "EHRPWM PWM support"
depends on ARCH_OMAP2PLUS || ARCH_DAVINCI_DA8XX
help
PWM driver support for the EHRPWM controller found on AM33XX
TI SOC
To compile this driver as a module, choose M here: the module
will be called pwm-tiehrpwm.
config PWM_TIPWMSS
bool
default y if (ARCH_OMAP2PLUS) && (PWM_TIECAP || PWM_TIEHRPWM)
help
PWM Subsystem driver support for AM33xx SOC.
PWM submodules require PWM config space access from submodule
drivers and require common parent driver support.
config PWM_TWL
tristate "TWL4030/6030 PWM support"
depends on TWL4030_CORE
help
Generic PWM framework driver for TWL4030/6030.
To compile this driver as a module, choose M here: the module
will be called pwm-twl.
config PWM_TWL_LED
tristate "TWL4030/6030 PWM support for LED drivers"
depends on TWL4030_CORE
help
Generic PWM framework driver for TWL4030/6030 LED terminals.
To compile this driver as a module, choose M here: the module
will be called pwm-twl-led.
config PWM_VT8500
tristate "vt8500 PWM support"
depends on ARCH_VT8500
help
Generic PWM framework driver for vt8500.
To compile this driver as a module, choose M here: the module
will be called pwm-vt8500.
endif
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