On Fri, 2009-10-09 at 14:01 +0530, Gautham R Shenoy wrote:
> Currently the cpu-allocation/deallocation process comprises of two steps:
> - Set the indicators and to update the device tree with DLPAR node
> information.
>
> - Online/offline the allocated/deallocated CPU.
>
> This is achieved by writing to the sysfs tunables "probe" during allocation
> and "release" during deallocation.
>
> At the sametime, the userspace can independently online/offline the CPUs of
> the system using the sysfs tunable "online".
>
> It is quite possible that when a userspace tool offlines a CPU
> for the purpose of deallocation and is in the process of updating the device
> tree, some other userspace tool could bring the CPU back online by writing to
> the "online" sysfs tunable thereby causing the deallocate process to fail.
>
> The solution to this is to serialize writes to the "probe/release" sysfs
> tunable with the writes to the "online" sysfs tunable.
>
> This patch employs a mutex to provide this serialization, which is a no-op on
> all architectures except PPC_PSERIES
>
> Signed-off-by: Gautham R Shenoy <e...@in.ibm.com>
Peter, did you get a chance to review this one ?
Cheers,
Ben.
> ---
> arch/powerpc/platforms/pseries/dlpar.c | 26 ++++++++++++++++++++++----
> drivers/base/cpu.c | 2 ++
> include/linux/cpu.h | 13 +++++++++++++
> 3 files changed, 37 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/dlpar.c
> b/arch/powerpc/platforms/pseries/dlpar.c
> index 9752386..fc261e6 100644
> --- a/arch/powerpc/platforms/pseries/dlpar.c
> +++ b/arch/powerpc/platforms/pseries/dlpar.c
> @@ -644,6 +644,18 @@ static ssize_t memory_release_store(struct class *class,
> const char *buf,
> return rc ? -1 : count;
> }
>
> +static DEFINE_MUTEX(pseries_cpu_hotplug_mutex);
> +
> +void cpu_hotplug_driver_lock()
> +{
> + mutex_lock(&pseries_cpu_hotplug_mutex);
> +}
> +
> +void cpu_hotplug_driver_unlock()
> +{
> + mutex_unlock(&pseries_cpu_hotplug_mutex);
> +}
> +
> static ssize_t cpu_probe_store(struct class *class, const char *buf,
> size_t count)
> {
> @@ -656,14 +668,15 @@ static ssize_t cpu_probe_store(struct class *class,
> const char *buf,
> if (rc)
> return -EINVAL;
>
> + cpu_hotplug_driver_lock();
> rc = acquire_drc(drc_index);
> if (rc)
> - return rc;
> + goto out;
>
> dn = configure_connector(drc_index);
> if (!dn) {
> release_drc(drc_index);
> - return rc;
> + goto out;
> }
>
> /* fixup dn name */
> @@ -672,7 +685,8 @@ static ssize_t cpu_probe_store(struct class *class, const
> char *buf,
> if (!cpu_name) {
> free_cc_nodes(dn);
> release_drc(drc_index);
> - return -ENOMEM;
> + rc = -ENOMEM;
> + goto out;
> }
>
> sprintf(cpu_name, "/cpus/%s", dn->full_name);
> @@ -684,6 +698,8 @@ static ssize_t cpu_probe_store(struct class *class, const
> char *buf,
> release_drc(drc_index);
>
> rc = online_node_cpus(dn);
> +out:
> + cpu_hotplug_driver_unlock();
>
> return rc ? rc : count;
> }
> @@ -705,6 +721,7 @@ static ssize_t cpu_release_store(struct class *class,
> const char *buf,
> return -EINVAL;
> }
>
> + cpu_hotplug_driver_lock();
> rc = offline_node_cpus(dn);
>
> if (rc)
> @@ -713,7 +730,7 @@ static ssize_t cpu_release_store(struct class *class,
> const char *buf,
> rc = release_drc(*drc_index);
> if (rc) {
> of_node_put(dn);
> - return rc;
> + goto out;
> }
>
> rc = remove_device_tree_nodes(dn);
> @@ -723,6 +740,7 @@ static ssize_t cpu_release_store(struct class *class,
> const char *buf,
> of_node_put(dn);
>
> out:
> + cpu_hotplug_driver_unlock();
> return rc ? rc : count;
> }
>
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index e62a4cc..07c3f05 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -35,6 +35,7 @@ static ssize_t __ref store_online(struct sys_device *dev,
> struct sysdev_attribut
> struct cpu *cpu = container_of(dev, struct cpu, sysdev);
> ssize_t ret;
>
> + cpu_hotplug_driver_lock();
> switch (buf[0]) {
> case '0':
> ret = cpu_down(cpu->sysdev.id);
> @@ -49,6 +50,7 @@ static ssize_t __ref store_online(struct sys_device *dev,
> struct sysdev_attribut
> default:
> ret = -EINVAL;
> }
> + cpu_hotplug_driver_unlock();
>
> if (ret >= 0)
> ret = count;
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 4753619..b0ad4e1 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -115,6 +115,19 @@ extern void put_online_cpus(void);
> #define unregister_hotcpu_notifier(nb) unregister_cpu_notifier(nb)
> int cpu_down(unsigned int cpu);
>
> +#ifdef CONFIG_PPC_PSERIES
> +extern void cpu_hotplug_driver_lock(void);
> +extern void cpu_hotplug_driver_unlock(void);
> +#else
> +static inline void cpu_hotplug_driver_lock(void)
> +{
> +}
> +
> +static inline void cpu_hotplug_driver_unlock(void)
> +{
> +}
> +#endif
> +
> #else /* CONFIG_HOTPLUG_CPU */
>
> #define get_online_cpus() do { } while (0)
>
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