From dd56af42bd829c6e770ed69812bd65a04eaeb1e4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 25 Aug 2014 20:25:06 -0700 Subject: rcu: Eliminate deadlock between CPU hotplug and expedited grace periods Currently, the expedited grace-period primitives do get_online_cpus(). This greatly simplifies their implementation, but means that calls to them holding locks that are acquired by CPU-hotplug notifiers (to say nothing of calls to these primitives from CPU-hotplug notifiers) can deadlock. But this is starting to become inconvenient, as can be seen here: https://lkml.org/lkml/2014/8/5/754. The problem in this case is that some developers need to acquire a mutex from a CPU-hotplug notifier, but also need to hold it across a synchronize_rcu_expedited(). As noted above, this currently results in deadlock. This commit avoids the deadlock and retains the simplicity by creating a try_get_online_cpus(), which returns false if the get_online_cpus() reference count could not immediately be incremented. If a call to try_get_online_cpus() returns true, the expedited primitives operate as before. If a call returns false, the expedited primitives fall back to normal grace-period operations. This falling back of course results in increased grace-period latency, but only during times when CPU hotplug operations are actually in flight. The effect should therefore be negligible during normal operation. Signed-off-by: Paul E. McKenney Cc: Josh Triplett Cc: "Rafael J. Wysocki" Tested-by: Lan Tianyu --- include/linux/cpu.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux/cpu.h') diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 95978ad7fcdd..b2d9a43012b2 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -213,6 +213,7 @@ extern struct bus_type cpu_subsys; extern void cpu_hotplug_begin(void); extern void cpu_hotplug_done(void); extern void get_online_cpus(void); +extern bool try_get_online_cpus(void); extern void put_online_cpus(void); extern void cpu_hotplug_disable(void); extern void cpu_hotplug_enable(void); @@ -230,6 +231,7 @@ int cpu_down(unsigned int cpu); static inline void cpu_hotplug_begin(void) {} static inline void cpu_hotplug_done(void) {} #define get_online_cpus() do { } while (0) +#define try_get_online_cpus() true #define put_online_cpus() do { } while (0) #define cpu_hotplug_disable() do { } while (0) #define cpu_hotplug_enable() do { } while (0) -- cgit v1.2.3-59-g8ed1b From 3d52943b3a51497a777e6d7d840a38596a92cee9 Mon Sep 17 00:00:00 2001 From: Sudeep Holla Date: Tue, 30 Sep 2014 14:48:24 +0100 Subject: drivers: base: add cpu_device_create to support per-cpu devices This patch adds a new function to create per-cpu devices. This helps in: 1. reusing the device infrastructure to create any cpu related attributes and corresponding sysfs instead of creating and dealing with raw kobjects directly 2. retaining the legacy path(/sys/devices/system/cpu/..) to support existing sysfs ABI 3. avoiding to create links in the bus directory pointing to the device as there would be per-cpu instance of these devices with the same name since dev->bus is not populated to cpu_sysbus on purpose Signed-off-by: Sudeep Holla Tested-by: Stephen Boyd Cc: Greg Kroah-Hartman Cc: David Herrmann Cc: Kay Sievers Signed-off-by: Greg Kroah-Hartman --- drivers/base/cpu.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/cpu.h | 4 ++++ 2 files changed, 58 insertions(+) (limited to 'include/linux/cpu.h') diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index 4d8a56406fbb..f829a4c71749 100644 --- a/drivers/base/cpu.c +++ b/drivers/base/cpu.c @@ -363,6 +363,60 @@ struct device *get_cpu_device(unsigned cpu) } EXPORT_SYMBOL_GPL(get_cpu_device); +static void device_create_release(struct device *dev) +{ + kfree(dev); +} + +static struct device * +__cpu_device_create(struct device *parent, void *drvdata, + const struct attribute_group **groups, + const char *fmt, va_list args) +{ + struct device *dev = NULL; + int retval = -ENODEV; + + dev = kzalloc(sizeof(*dev), GFP_KERNEL); + if (!dev) { + retval = -ENOMEM; + goto error; + } + + device_initialize(dev); + dev->parent = parent; + dev->groups = groups; + dev->release = device_create_release; + dev_set_drvdata(dev, drvdata); + + retval = kobject_set_name_vargs(&dev->kobj, fmt, args); + if (retval) + goto error; + + retval = device_add(dev); + if (retval) + goto error; + + return dev; + +error: + put_device(dev); + return ERR_PTR(retval); +} + +struct device *cpu_device_create(struct device *parent, void *drvdata, + const struct attribute_group **groups, + const char *fmt, ...) +{ + va_list vargs; + struct device *dev; + + va_start(vargs, fmt); + dev = __cpu_device_create(parent, drvdata, groups, fmt, vargs); + va_end(vargs); + return dev; +} +EXPORT_SYMBOL_GPL(cpu_device_create); + #ifdef CONFIG_GENERIC_CPU_AUTOPROBE static DEVICE_ATTR(modalias, 0444, print_cpu_modalias, NULL); #endif diff --git a/include/linux/cpu.h b/include/linux/cpu.h index b2d9a43012b2..4260e8594bd7 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -19,6 +19,7 @@ struct device; struct device_node; +struct attribute_group; struct cpu { int node_id; /* The node which contains the CPU */ @@ -39,6 +40,9 @@ extern void cpu_remove_dev_attr(struct device_attribute *attr); extern int cpu_add_dev_attr_group(struct attribute_group *attrs); extern void cpu_remove_dev_attr_group(struct attribute_group *attrs); +extern struct device *cpu_device_create(struct device *parent, void *drvdata, + const struct attribute_group **groups, + const char *fmt, ...); #ifdef CONFIG_HOTPLUG_CPU extern void unregister_cpu(struct cpu *cpu); extern ssize_t arch_cpu_probe(const char *, size_t); -- cgit v1.2.3-59-g8ed1b