On Thu, Feb 16, 2017 at 7:08 PM, Ross Zwisler
<ross.zwisler@xxxxxxxxxxxxxxx> wrote:
> On Thu, Feb 16, 2017 at 01:53:58PM -0800, Dan Williams wrote:
>> mem_hotplug_begin() assumes that it can set mem_hotplug.active_writer
>> and run the hotplug process without racing another thread. Validate this
>> assumption with a lockdep assertion.
>>
>> Cc: Michal Hocko <mhocko@xxxxxxxx>
>> Cc: Toshi Kani <toshi.kani@xxxxxxx>
>> Cc: Vlastimil Babka <vbabka@xxxxxxx>
>> Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> Reported-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
>> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
>> ---
>> drivers/base/core.c | 5 +++++
>> include/linux/device.h | 1 +
>> mm/memory_hotplug.c | 2 ++
>> 3 files changed, 8 insertions(+)
>>
>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>> index 8c25e68e67d7..3050e6f99403 100644
>> --- a/drivers/base/core.c
>> +++ b/drivers/base/core.c
>> @@ -638,6 +638,11 @@ int lock_device_hotplug_sysfs(void)
>> return restart_syscall();
>> }
>>
>> +void assert_held_device_hotplug(void)
>> +{
>> + lockdep_assert_held(&device_hotplug_lock);
>> +}
>> +
>> #ifdef CONFIG_BLOCK
>> static inline int device_is_not_partition(struct device *dev)
>> {
>> diff --git a/include/linux/device.h b/include/linux/device.h
>> index 491b4c0ca633..815965ee55dd 100644
>> --- a/include/linux/device.h
>> +++ b/include/linux/device.h
>> @@ -1135,6 +1135,7 @@ static inline bool device_supports_offline(struct device *dev)
>> extern void lock_device_hotplug(void);
>> extern void unlock_device_hotplug(void);
>> extern int lock_device_hotplug_sysfs(void);
>> +void assert_held_device_hotplug(void);
>> extern int device_offline(struct device *dev);
>> extern int device_online(struct device *dev);
>> extern void set_primary_fwnode(struct device *dev, struct fwnode_handle *fwnode);
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index b8c11e063ff0..1635a2a085e5 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -126,6 +126,8 @@ void put_online_mems(void)
>>
>> void mem_hotplug_begin(void)
>> {
>> + assert_held_device_hotplug();
>
> What's the benefit to defining assert_held_device_hotplug() as a one line
> wrapper, instead of just calling lockdep_assert_held(&device_hotplug_lock)
> directly?
>
This allows us to keep device_hotplug_lock statically defined and an
internal implementation detail of the device core.
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