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?
> +
> mem_hotplug.active_writer = current;
>
> memhp_lock_acquire();
>
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