diff options
author | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-12-18 10:53:12 +0000 |
---|---|---|
committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-12-20 15:09:13 +0000 |
commit | 3705ff6da538aff6dba535e2e9cbcbb9456d0d53 (patch) | |
tree | 348fcec2be9d41e1839686a6c03f0b5479d7e4f9 /arch/arm/mach-s5pv310/platsmp.c | |
parent | ed3768a8d9dc2d345d4f27eb44ee1e4825056c08 (diff) |
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 <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/mach-s5pv310/platsmp.c')
-rw-r--r-- | arch/arm/mach-s5pv310/platsmp.c | 20 |
1 files changed, 15 insertions, 5 deletions
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 |