Patchwork ARM: smp: call platform's cpu_die in ipi_cpu_stop

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Submitter Russell King - ARM Linux
Date April 18, 2013, 7:09 p.m.
Message ID <20130418190923.GE14496@n2100.arm.linux.org.uk>
Download mbox | patch
Permalink /patch/237721/
State New
Headers show

Comments

Russell King - ARM Linux - April 18, 2013, 7:09 p.m.
On Thu, Apr 18, 2013 at 07:25:34PM +0100, Russell King - ARM Linux wrote:
> On Thu, Apr 18, 2013 at 06:18:01PM +0100, Russell King - ARM Linux wrote:
> > On Sat, Apr 06, 2013 at 03:37:04PM +0300, Kevin Bracey wrote:
> > > When hotplugging out, both cpu_kill and cpu_die have always been called.
> > > But when smp_send_stop was used in machine_shutdown or panic, only
> > > cpu_kill was called.
> > > 
> > > This causes problems for co-ordination between cpu_kill and cpu_die, as
> > > attempted by shmobile. So add cpu_die call to ipi_cpu_stop, to ensure
> > > that cpu_kill and cpu_die calls always occur together.
> > 
> > Actually, I'd prefer to pull more code out of the platforms.  Now
> > that we have flush_cache_louis(), we can flush the L1 cache for the
> > CPU going down in cpu_die() itself.  We just need to be careful
> > with that complete() call to ensure that becomes visible to other
> > cores before power is cut to the L1 cache.
> > 
> > That's fine though - because it must become visible for __cpu_die()
> > to continue (otherwise it will time out).
> > 
> > That should render shmobile's cpu_dead thing unnecessary, because the
> > platform independent code will do the required synchronisation.
> 
> So, something like the below (which is a combined patch of three).  The
> key points here being that:
> 
> 1. We flush the L1 cache in cpu_die(), which pushes any dirty cache lines
>    out of the L1 cache and invalidates it.  At the point this function
>    completes, any data in the L1 cache has been pushed out and all
>    cache lines are invalid.
> 2. We complete(), which allows __cpu_die() to proceed and call
>    platform_cpu_kill().  This may create dirty cache lines which this
>    CPU exclusively owns, but the CPU in __cpu_die() will gain those
>    cache lines before wait_for_completion() can return - not only the
>    completion counter but also the spinlock, which this CPU will have
>    ended up reading and writing - and so can no longer be owned by the
>    dying CPU.
> 3. The following mb() is belt and braces to ensure that the completion
>    is visible.  It isn't strictly required because the spinlocks will
>    do the necessary stuff to ensure this.
> 4. Any dirtying of the cache after this rellay doesn't matter _if_ only
>    the stack is touched, or other data is only read.
> 5. I've left those platforms which disable the L1 cache, then flush
>    alone; that _should_ be removable with this patch as well, but as
>    a separate patch.
> 
> Now, with this patch applied, we guarantee that we push out any data
> that matters from the dying CPU before platform_cpu_kill() is called.
> That should mean that shmobile can remove that whole cpu_dead thing.
> 
> I've tested this on OMAP, and it appears to work from a simple test of
> CPU hotplug.  This patch(set) also kills the cpu_disable() that tegra
> has which is just a copy of the generic version.

Okay, last version for tonight, with additional comments too, and a
hole plugged if the powering down is done by the platform via
cpu_die().

 arch/arm/kernel/smp.c               |   42 +++++++++++++++++++++++++++++++---
 arch/arm/mach-exynos/hotplug.c      |    1 -
 arch/arm/mach-highbank/hotplug.c    |    4 ---
 arch/arm/mach-imx/hotplug.c         |    2 -
 arch/arm/mach-msm/hotplug.c         |    4 ---
 arch/arm/mach-omap2/omap-hotplug.c  |    3 --
 arch/arm/mach-prima2/hotplug.c      |    3 --
 arch/arm/mach-realview/hotplug.c    |    2 -
 arch/arm/mach-shmobile/smp-sh73a0.c |    8 ------
 arch/arm/mach-spear13xx/hotplug.c   |    2 -
 arch/arm/mach-tegra/common.h        |    1 -
 arch/arm/mach-tegra/hotplug.c       |   10 --------
 arch/arm/mach-tegra/platsmp.c       |    1 -
 arch/arm/mach-ux500/hotplug.c       |    3 --
 arch/arm/mach-vexpress/hotplug.c    |    2 -
 15 files changed, 38 insertions(+), 50 deletions(-)
Rob Herring - May 1, 2013, 1:06 p.m.
On Thu, Apr 18, 2013 at 2:09 PM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Thu, Apr 18, 2013 at 07:25:34PM +0100, Russell King - ARM Linux wrote:
>> On Thu, Apr 18, 2013 at 06:18:01PM +0100, Russell King - ARM Linux wrote:
>> > On Sat, Apr 06, 2013 at 03:37:04PM +0300, Kevin Bracey wrote:

[...]

>> Now, with this patch applied, we guarantee that we push out any data
>> that matters from the dying CPU before platform_cpu_kill() is called.
>> That should mean that shmobile can remove that whole cpu_dead thing.
>>
>> I've tested this on OMAP, and it appears to work from a simple test of
>> CPU hotplug.  This patch(set) also kills the cpu_disable() that tegra
>> has which is just a copy of the generic version.
>
> Okay, last version for tonight, with additional comments too, and a
> hole plugged if the powering down is done by the platform via
> cpu_die().
>
>  arch/arm/kernel/smp.c               |   42 +++++++++++++++++++++++++++++++---
>  arch/arm/mach-exynos/hotplug.c      |    1 -
>  arch/arm/mach-highbank/hotplug.c    |    4 ---

Looks like this just landed in -next and it breaks highbank build.
Run-time will also be broken. See the last commit to this file in
final 3.9 which will also conflict with this one. The problem is that
highbank_set_cpu_jump calls outer cache functions which take a
spinlock and pollute the L1 cache. This all goes away once PCSI
support goes in, but for now we need another spot to clear the jump
address or just drop the highbank change.

Rob
Russell King - ARM Linux - May 2, 2013, 5:55 p.m.
On Wed, May 01, 2013 at 08:06:56AM -0500, Rob Herring wrote:
> On Thu, Apr 18, 2013 at 2:09 PM, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
> > On Thu, Apr 18, 2013 at 07:25:34PM +0100, Russell King - ARM Linux wrote:
> >> On Thu, Apr 18, 2013 at 06:18:01PM +0100, Russell King - ARM Linux wrote:
> >> > On Sat, Apr 06, 2013 at 03:37:04PM +0300, Kevin Bracey wrote:
> 
> [...]
> 
> >> Now, with this patch applied, we guarantee that we push out any data
> >> that matters from the dying CPU before platform_cpu_kill() is called.
> >> That should mean that shmobile can remove that whole cpu_dead thing.
> >>
> >> I've tested this on OMAP, and it appears to work from a simple test of
> >> CPU hotplug.  This patch(set) also kills the cpu_disable() that tegra
> >> has which is just a copy of the generic version.
> >
> > Okay, last version for tonight, with additional comments too, and a
> > hole plugged if the powering down is done by the platform via
> > cpu_die().
> >
> >  arch/arm/kernel/smp.c               |   42 +++++++++++++++++++++++++++++++---
> >  arch/arm/mach-exynos/hotplug.c      |    1 -
> >  arch/arm/mach-highbank/hotplug.c    |    4 ---
> 
> Looks like this just landed in -next and it breaks highbank build.
> Run-time will also be broken. See the last commit to this file in
> final 3.9 which will also conflict with this one. The problem is that
> highbank_set_cpu_jump calls outer cache functions which take a
> spinlock and pollute the L1 cache. This all goes away once PCSI
> support goes in, but for now we need another spot to clear the jump
> address or just drop the highbank change.

If that's the case then what you currently have is dangerous.  There
is no guarantee that the results of touching those locks will get
flushed out of the L1 cache of the going-down CPU - you _could_ end
up with the result of the lock being flushed out but not the unlock,
which would lead to a system deadlock.

The only thing which has changed as far as highbank is concerned is
that it will now use flush_cache_louis() rather than flush_cache_all()
before calling highbank_set_cpu_jump().

So, I think this has merely uncovered a latent bug in your code. :)

Patch

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 1f2cccc..4231034 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -211,6 +211,13 @@  void __cpuinit __cpu_die(unsigned int cpu)
 	}
 	printk(KERN_NOTICE "CPU%u: shutdown\n", cpu);
 
+	/*
+	 * platform_cpu_kill() is generally expected to do the powering off
+	 * and/or cutting of clocks to the dying CPU.  Optionally, this may
+	 * be done by the CPU which is dying in preference to supporting
+	 * this call, but that means there is _no_ synchronisation between
+	 * the requesting CPU and the dying CPU actually losing power.
+	 */
 	if (!platform_cpu_kill(cpu))
 		printk("CPU%u: unable to kill\n", cpu);
 }
@@ -230,14 +237,41 @@  void __ref cpu_die(void)
 	idle_task_exit();
 
 	local_irq_disable();
-	mb();
 
-	/* Tell __cpu_die() that this CPU is now safe to dispose of */
+	/*
+	 * Flush the data out of the L1 cache for this CPU.  This must be
+	 * before the completion to ensure that data is safely written out
+	 * before platform_cpu_kill() gets called - which may disable
+	 * *this* CPU and power down its cache.
+	 */
+	flush_cache_louis();
+
+	/*
+	 * Tell __cpu_die() that this CPU is now safe to dispose of.  Once
+	 * this returns, power and/or clocks can be removed at any point
+	 * from this CPU and its cache by platform_cpu_kill().
+	 */
 	RCU_NONIDLE(complete(&cpu_died));
 
 	/*
-	 * actual CPU shutdown procedure is at least platform (if not
-	 * CPU) specific.
+	 * Ensure that the cache lines associated with that completion are
+	 * written out.  This covers the case where _this_ CPU is doing the
+	 * powering down, to ensure that the completion is visible to the
+	 * CPU waiting for this one.
+	 */
+	flush_cache_louis();
+
+	/*
+	 * The actual CPU shutdown procedure is at least platform (if not
+	 * CPU) specific.  This may remove power, or it may simply spin.
+	 *
+	 * Platforms are generally expected *NOT* to return from this call,
+	 * although there are some which do because they have no way to
+	 * power down the CPU.  These platforms are the _only_ reason we
+	 * have a return path which uses the fragment of assembly below.
+	 *
+	 * The return path should not be used for platforms which can
+	 * power off the CPU.
 	 */
 	if (smp_ops.cpu_die)
 		smp_ops.cpu_die(cpu);
diff --git a/arch/arm/mach-exynos/hotplug.c b/arch/arm/mach-exynos/hotplug.c
index c3f825b..af90cfa 100644
--- a/arch/arm/mach-exynos/hotplug.c
+++ b/arch/arm/mach-exynos/hotplug.c
@@ -28,7 +28,6 @@  static inline void cpu_enter_lowpower_a9(void)
 {
 	unsigned int v;
 
-	flush_cache_all();
 	asm volatile(
 	"	mcr	p15, 0, %1, c7, c5, 0\n"
 	"	mcr	p15, 0, %1, c7, c10, 4\n"
diff --git a/arch/arm/mach-highbank/hotplug.c b/arch/arm/mach-highbank/hotplug.c
index f30c528..35dd42e 100644
--- a/arch/arm/mach-highbank/hotplug.c
+++ b/arch/arm/mach-highbank/hotplug.c
@@ -15,8 +15,6 @@ 
  */
 #include <linux/kernel.h>
 
-#include <asm/cacheflush.h>
-
 #include "core.h"
 #include "sysregs.h"
 
@@ -28,8 +26,6 @@  extern void secondary_startup(void);
  */
 void __ref highbank_cpu_die(unsigned int cpu)
 {
-	flush_cache_all();
-
 	highbank_set_cpu_jump(cpu, phys_to_virt(0));
 	highbank_set_core_pwr();
 
diff --git a/arch/arm/mach-imx/hotplug.c b/arch/arm/mach-imx/hotplug.c
index 361a253..5e91112 100644
--- a/arch/arm/mach-imx/hotplug.c
+++ b/arch/arm/mach-imx/hotplug.c
@@ -11,7 +11,6 @@ 
  */
 
 #include <linux/errno.h>
-#include <asm/cacheflush.h>
 #include <asm/cp15.h>
 
 #include "common.h"
@@ -20,7 +19,6 @@  static inline void cpu_enter_lowpower(void)
 {
 	unsigned int v;
 
-	flush_cache_all();
 	asm volatile(
 		"mcr	p15, 0, %1, c7, c5, 0\n"
 	"	mcr	p15, 0, %1, c7, c10, 4\n"
diff --git a/arch/arm/mach-msm/hotplug.c b/arch/arm/mach-msm/hotplug.c
index 750446f..326a872 100644
--- a/arch/arm/mach-msm/hotplug.c
+++ b/arch/arm/mach-msm/hotplug.c
@@ -10,16 +10,12 @@ 
 #include <linux/errno.h>
 #include <linux/smp.h>
 
-#include <asm/cacheflush.h>
 #include <asm/smp_plat.h>
 
 #include "common.h"
 
 static inline void cpu_enter_lowpower(void)
 {
-	/* Just flush the cache. Changing the coherency is not yet
-	 * available on msm. */
-	flush_cache_all();
 }
 
 static inline void cpu_leave_lowpower(void)
diff --git a/arch/arm/mach-omap2/omap-hotplug.c b/arch/arm/mach-omap2/omap-hotplug.c
index e712d17..ceb30a5 100644
--- a/arch/arm/mach-omap2/omap-hotplug.c
+++ b/arch/arm/mach-omap2/omap-hotplug.c
@@ -35,9 +35,6 @@  void __ref omap4_cpu_die(unsigned int cpu)
 	unsigned int boot_cpu = 0;
 	void __iomem *base = omap_get_wakeupgen_base();
 
-	flush_cache_all();
-	dsb();
-
 	/*
 	 * we're ready for shutdown now, so do it
 	 */
diff --git a/arch/arm/mach-prima2/hotplug.c b/arch/arm/mach-prima2/hotplug.c
index f4b17cb..0ab2f8b 100644
--- a/arch/arm/mach-prima2/hotplug.c
+++ b/arch/arm/mach-prima2/hotplug.c
@@ -10,13 +10,10 @@ 
 #include <linux/errno.h>
 #include <linux/smp.h>
 
-#include <asm/cacheflush.h>
 #include <asm/smp_plat.h>
 
 static inline void platform_do_lowpower(unsigned int cpu)
 {
-	flush_cache_all();
-
 	/* we put the platform to just WFI */
 	for (;;) {
 		__asm__ __volatile__("dsb\n\t" "wfi\n\t"
diff --git a/arch/arm/mach-realview/hotplug.c b/arch/arm/mach-realview/hotplug.c
index 53818e5..ac22dd4 100644
--- a/arch/arm/mach-realview/hotplug.c
+++ b/arch/arm/mach-realview/hotplug.c
@@ -12,7 +12,6 @@ 
 #include <linux/errno.h>
 #include <linux/smp.h>
 
-#include <asm/cacheflush.h>
 #include <asm/cp15.h>
 #include <asm/smp_plat.h>
 
@@ -20,7 +19,6 @@  static inline void cpu_enter_lowpower(void)
 {
 	unsigned int v;
 
-	flush_cache_all();
 	asm volatile(
 	"	mcr	p15, 0, %1, c7, c5, 0\n"
 	"	mcr	p15, 0, %1, c7, c10, 4\n"
diff --git a/arch/arm/mach-shmobile/smp-sh73a0.c b/arch/arm/mach-shmobile/smp-sh73a0.c
index acb46a9..2f1ef1b 100644
--- a/arch/arm/mach-shmobile/smp-sh73a0.c
+++ b/arch/arm/mach-shmobile/smp-sh73a0.c
@@ -119,14 +119,6 @@  static int sh73a0_cpu_kill(unsigned int cpu)
 
 static void sh73a0_cpu_die(unsigned int cpu)
 {
-	/*
-	 * The ARM MPcore does not issue a cache coherency request for the L1
-	 * cache when powering off single CPUs. We must take care of this and
-	 * further caches.
-	 */
-	dsb();
-	flush_cache_all();
-
 	/* Set power off mode. This takes the CPU out of the MP cluster */
 	scu_power_mode(scu_base_addr(), SCU_PM_POWEROFF);
 
diff --git a/arch/arm/mach-spear13xx/hotplug.c b/arch/arm/mach-spear13xx/hotplug.c
index a7d2dd1..d97749c 100644
--- a/arch/arm/mach-spear13xx/hotplug.c
+++ b/arch/arm/mach-spear13xx/hotplug.c
@@ -13,7 +13,6 @@ 
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/smp.h>
-#include <asm/cacheflush.h>
 #include <asm/cp15.h>
 #include <asm/smp_plat.h>
 
@@ -21,7 +20,6 @@  static inline void cpu_enter_lowpower(void)
 {
 	unsigned int v;
 
-	flush_cache_all();
 	asm volatile(
 	"	mcr	p15, 0, %1, c7, c5, 0\n"
 	"	dsb\n"
diff --git a/arch/arm/mach-tegra/common.h b/arch/arm/mach-tegra/common.h
index 32f8eb3..5900cc4 100644
--- a/arch/arm/mach-tegra/common.h
+++ b/arch/arm/mach-tegra/common.h
@@ -2,4 +2,3 @@  extern struct smp_operations tegra_smp_ops;
 
 extern int tegra_cpu_kill(unsigned int cpu);
 extern void tegra_cpu_die(unsigned int cpu);
-extern int tegra_cpu_disable(unsigned int cpu);
diff --git a/arch/arm/mach-tegra/hotplug.c b/arch/arm/mach-tegra/hotplug.c
index a599f6e..e8323bc 100644
--- a/arch/arm/mach-tegra/hotplug.c
+++ b/arch/arm/mach-tegra/hotplug.c
@@ -12,7 +12,6 @@ 
 #include <linux/smp.h>
 #include <linux/clk/tegra.h>
 
-#include <asm/cacheflush.h>
 #include <asm/smp_plat.h>
 
 #include "sleep.h"
@@ -47,15 +46,6 @@  void __ref tegra_cpu_die(unsigned int cpu)
 	BUG();
 }
 
-int tegra_cpu_disable(unsigned int cpu)
-{
-	/*
-	 * we don't allow CPU 0 to be shutdown (it is still too special
-	 * e.g. clock tick interrupts)
-	 */
-	return cpu == 0 ? -EPERM : 0;
-}
-
 #ifdef CONFIG_ARCH_TEGRA_2x_SOC
 extern void tegra20_hotplug_shutdown(void);
 void __init tegra20_hotplug_init(void)
diff --git a/arch/arm/mach-tegra/platsmp.c b/arch/arm/mach-tegra/platsmp.c
index 2c6b3d5..ec33ec8 100644
--- a/arch/arm/mach-tegra/platsmp.c
+++ b/arch/arm/mach-tegra/platsmp.c
@@ -192,6 +192,5 @@  struct smp_operations tegra_smp_ops __initdata = {
 #ifdef CONFIG_HOTPLUG_CPU
 	.cpu_kill		= tegra_cpu_kill,
 	.cpu_die		= tegra_cpu_die,
-	.cpu_disable		= tegra_cpu_disable,
 #endif
 };
diff --git a/arch/arm/mach-ux500/hotplug.c b/arch/arm/mach-ux500/hotplug.c
index 2f6af25..1c55a55 100644
--- a/arch/arm/mach-ux500/hotplug.c
+++ b/arch/arm/mach-ux500/hotplug.c
@@ -12,7 +12,6 @@ 
 #include <linux/errno.h>
 #include <linux/smp.h>
 
-#include <asm/cacheflush.h>
 #include <asm/smp_plat.h>
 
 #include <mach/setup.h>
@@ -24,8 +23,6 @@ 
  */
 void __ref ux500_cpu_die(unsigned int cpu)
 {
-	flush_cache_all();
-
 	/* directly enter low power state, skipping secure registers */
 	for (;;) {
 		__asm__ __volatile__("dsb\n\t" "wfi\n\t"
diff --git a/arch/arm/mach-vexpress/hotplug.c b/arch/arm/mach-vexpress/hotplug.c
index a141b98..f0ce6b8 100644
--- a/arch/arm/mach-vexpress/hotplug.c
+++ b/arch/arm/mach-vexpress/hotplug.c
@@ -12,7 +12,6 @@ 
 #include <linux/errno.h>
 #include <linux/smp.h>
 
-#include <asm/cacheflush.h>
 #include <asm/smp_plat.h>
 #include <asm/cp15.h>
 
@@ -20,7 +19,6 @@  static inline void cpu_enter_lowpower(void)
 {
 	unsigned int v;
 
-	flush_cache_all();
 	asm volatile(
 		"mcr	p15, 0, %1, c7, c5, 0\n"
 	"	mcr	p15, 0, %1, c7, c10, 4\n"