From 3705ff6da538aff6dba535e2e9cbcbb9456d0d53 Mon Sep 17 00:00:00 2001 From: Russell King Date: Sat, 18 Dec 2010 10:53:12 +0000 Subject: ARM: Fix subtle race in CPU pen_release hotplug code There is a subtle race in the CPU hotplug code, where a CPU which has been offlined can online itself before being requested, which results in things going astray on the next online/offline cycle. What happens in the normal online/offline/online cycle is: CPU0 CPU3 requests boot of CPU3 pen_release = 3 flush cache line checks pen_release, reads 3 starts boot pen_release = -1 ... requests CPU3 offline ... ... dies ... checks pen_release, reads -1 requests boot of CPU3 pen_release = 3 flush cache line checks pen_release, reads 3 starts boot pen_release = -1 However, as the write of -1 of pen_release is not fully flushed back to memory, and the checking of pen_release is done with caches disabled, this allows CPU3 the opportunity to read the old value of pen_release: CPU0 CPU3 requests boot of CPU3 pen_release = 3 flush cache line checks pen_release, reads 3 starts boot pen_release = -1 ... requests CPU3 offline ... ... dies ... checks pen_release, reads 3 starts boot pen_release = -1 requests boot of CPU3 pen_release = 3 flush cache line Fix this by grouping the write of pen_release along with its cache line flushing code to ensure that any update to pen_release is always pushed out to physical memory. Signed-off-by: Russell King --- arch/arm/mach-realview/platsmp.c | 19 +++++++++++++++---- arch/arm/mach-s5pv310/platsmp.c | 20 +++++++++++++++----- arch/arm/mach-ux500/platsmp.c | 22 +++++++++++++++------- arch/arm/mach-vexpress/platsmp.c | 20 +++++++++++++++----- 4 files changed, 60 insertions(+), 21 deletions(-) (limited to 'arch/arm') diff --git a/arch/arm/mach-realview/platsmp.c b/arch/arm/mach-realview/platsmp.c index 226c63102a0..bb8d6c4e431 100644 --- a/arch/arm/mach-realview/platsmp.c +++ b/arch/arm/mach-realview/platsmp.c @@ -36,6 +36,19 @@ extern void realview_secondary_startup(void); */ volatile int __cpuinitdata pen_release = -1; +/* + * Write pen_release in a way that is guaranteed to be visible to all + * observers, irrespective of whether they're taking part in coherency + * or not. This is necessary for the hotplug code to work reliably. + */ +static void write_pen_release(int val) +{ + pen_release = val; + smp_wmb(); + __cpuc_flush_dcache_area((void *)&pen_release, sizeof(pen_release)); + outer_clean_range(__pa(&pen_release), __pa(&pen_release + 1)); +} + static void __iomem *scu_base_addr(void) { if (machine_is_realview_eb_mp()) @@ -64,8 +77,7 @@ void __cpuinit platform_secondary_init(unsigned int cpu) * let the primary processor know we're out of the * pen, then head off into the C entry point */ - pen_release = -1; - smp_wmb(); + write_pen_release(-1); /* * Synchronise with the boot thread. @@ -92,8 +104,7 @@ int __cpuinit boot_secondary(unsigned int cpu, struct task_struct *idle) * Note that "pen_release" is the hardware CPU ID, whereas * "cpu" is Linux's internal ID. */ - pen_release = cpu; - flush_cache_all(); + write_pen_release(cpu); /* * Send the secondary CPU a soft interrupt, thereby causing diff --git a/arch/arm/mach-s5pv310/platsmp.c b/arch/arm/mach-s5pv310/platsmp.c index 18aaf5f5403..98c04748ed8 100644 --- a/arch/arm/mach-s5pv310/platsmp.c +++ b/arch/arm/mach-s5pv310/platsmp.c @@ -37,6 +37,19 @@ extern void s5pv310_secondary_startup(void); volatile int __cpuinitdata pen_release = -1; +/* + * Write pen_release in a way that is guaranteed to be visible to all + * observers, irrespective of whether they're taking part in coherency + * or not. This is necessary for the hotplug code to work reliably. + */ +static void write_pen_release(int val) +{ + pen_release = val; + smp_wmb(); + __cpuc_flush_dcache_area((void *)&pen_release, sizeof(pen_release)); + outer_clean_range(__pa(&pen_release), __pa(&pen_release + 1)); +} + static void __iomem *scu_base_addr(void) { return (void __iomem *)(S5P_VA_SCU); @@ -57,8 +70,7 @@ void __cpuinit platform_secondary_init(unsigned int cpu) * let the primary processor know we're out of the * pen, then head off into the C entry point */ - pen_release = -1; - smp_wmb(); + write_pen_release(-1); /* * Synchronise with the boot thread. @@ -85,9 +97,7 @@ int __cpuinit boot_secondary(unsigned int cpu, struct task_struct *idle) * Note that "pen_release" is the hardware CPU ID, whereas * "cpu" is Linux's internal ID. */ - pen_release = cpu; - __cpuc_flush_dcache_area((void *)&pen_release, sizeof(pen_release)); - outer_clean_range(__pa(&pen_release), __pa(&pen_release + 1)); + write_pen_release(cpu); /* * Send the secondary CPU a soft interrupt, thereby causing diff --git a/arch/arm/mach-ux500/platsmp.c b/arch/arm/mach-ux500/platsmp.c index ddedbc80c41..f71175a766d 100644 --- a/arch/arm/mach-ux500/platsmp.c +++ b/arch/arm/mach-ux500/platsmp.c @@ -27,6 +27,19 @@ */ volatile int __cpuinitdata pen_release = -1; +/* + * Write pen_release in a way that is guaranteed to be visible to all + * observers, irrespective of whether they're taking part in coherency + * or not. This is necessary for the hotplug code to work reliably. + */ +static void write_pen_release(int val) +{ + pen_release = val; + smp_wmb(); + __cpuc_flush_dcache_area((void *)&pen_release, sizeof(pen_release)); + outer_clean_range(__pa(&pen_release), __pa(&pen_release + 1)); +} + static DEFINE_SPINLOCK(boot_lock); void __cpuinit platform_secondary_init(unsigned int cpu) @@ -42,7 +55,7 @@ void __cpuinit platform_secondary_init(unsigned int cpu) * let the primary processor know we're out of the * pen, then head off into the C entry point */ - pen_release = -1; + write_pen_release(-1); /* * Synchronise with the boot thread. @@ -66,9 +79,7 @@ int __cpuinit boot_secondary(unsigned int cpu, struct task_struct *idle) * the holding pen - release it, then wait for it to flag * that it has been released by resetting pen_release. */ - pen_release = cpu; - __cpuc_flush_dcache_area((void *)&pen_release, sizeof(pen_release)); - outer_clean_range(__pa(&pen_release), __pa(&pen_release) + 1); + write_pen_release(cpu); smp_cross_call(cpumask_of(cpu), 1); @@ -89,9 +100,6 @@ int __cpuinit boot_secondary(unsigned int cpu, struct task_struct *idle) static void __init wakeup_secondary(void) { - /* nobody is to be released from the pen yet */ - pen_release = -1; - /* * write the address of secondary startup into the backup ram register * at offset 0x1FF4, then write the magic number 0xA1FEED01 to the diff --git a/arch/arm/mach-vexpress/platsmp.c b/arch/arm/mach-vexpress/platsmp.c index d7e0cb994e9..8ce9fef2955 100644 --- a/arch/arm/mach-vexpress/platsmp.c +++ b/arch/arm/mach-vexpress/platsmp.c @@ -34,6 +34,19 @@ extern void vexpress_secondary_startup(void); */ volatile int __cpuinitdata pen_release = -1; +/* + * Write pen_release in a way that is guaranteed to be visible to all + * observers, irrespective of whether they're taking part in coherency + * or not. This is necessary for the hotplug code to work reliably. + */ +static void write_pen_release(int val) +{ + pen_release = val; + smp_wmb(); + __cpuc_flush_dcache_area((void *)&pen_release, sizeof(pen_release)); + outer_clean_range(__pa(&pen_release), __pa(&pen_release + 1)); +} + static void __iomem *scu_base_addr(void) { return MMIO_P2V(A9_MPCORE_SCU); @@ -54,8 +67,7 @@ void __cpuinit platform_secondary_init(unsigned int cpu) * let the primary processor know we're out of the * pen, then head off into the C entry point */ - pen_release = -1; - smp_wmb(); + write_pen_release(-1); /* * Synchronise with the boot thread. @@ -80,9 +92,7 @@ int __cpuinit boot_secondary(unsigned int cpu, struct task_struct *idle) * since we haven't sent them a soft interrupt, they shouldn't * be there. */ - pen_release = cpu; - __cpuc_flush_dcache_area((void *)&pen_release, sizeof(pen_release)); - outer_clean_range(__pa(&pen_release), __pa(&pen_release + 1)); + write_pen_release(cpu); /* * Send the secondary CPU a soft interrupt, thereby causing -- cgit v1.2.3