Re: [Xen-devel] [PATCH v1 2/6] mm/memory_hotplug: make add_memory() take the device_hotplug_lock

["Rafael J. Wysocki" <rafael@xxxxxxxxxx>]

On Tue, Sep 18, 2018 at 1:48 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> add_memory() currently does not take the device_hotplug_lock, however
> is aleady called under the lock from
>         arch/powerpc/platforms/pseries/hotplug-memory.c
>         drivers/acpi/acpi_memhotplug.c
> to synchronize against CPU hot-remove and similar.
>
> In general, we should hold the device_hotplug_lock when adding memory
> to synchronize against online/offline request (e.g. from user space) -
> which already resulted in lock inversions due to device_lock() and
> mem_hotplug_lock - see 30467e0b3be ("mm, hotplug: fix concurrent memory
> hot-add deadlock"). add_memory()/add_memory_resource() will create memory
> block devices, so this really feels like the right thing to do.
>
> Holding the device_hotplug_lock makes sure that a memory block device
> can really only be accessed (e.g. via .online/.state) from user space,
> once the memory has been fully added to the system.
>
> The lock is not held yet in
>         drivers/xen/balloon.c
>         arch/powerpc/platforms/powernv/memtrace.c
>         drivers/s390/char/sclp_cmd.c
>         drivers/hv/hv_balloon.c
> So, let's either use the locked variants or take the lock.
>
> Don't export add_memory_resource(), as it once was exported to be used
> by XEN, which is never built as a module. If somebody requires it, we
> also have to export a locked variant (as device_hotplug_lock is never
> exported).
>
> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> Cc: Len Brown <lenb@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: Nathan Fontenot <nfont@xxxxxxxxxxxxxxxxxx>
> Cc: John Allen <jallen@xxxxxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Mathieu Malaterre <malat@xxxxxxxxxx>
> Cc: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx>
> Cc: YASUAKI ISHIMATSU <yasu.isimatu@xxxxxxxxx>
> Reviewed-by: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
>  .../platforms/pseries/hotplug-memory.c        |  2 +-
>  drivers/acpi/acpi_memhotplug.c                |  2 +-
>  drivers/base/memory.c                         |  9 ++++++--
>  drivers/xen/balloon.c                         |  3 +++
>  include/linux/memory_hotplug.h                |  1 +
>  mm/memory_hotplug.c                           | 22 ++++++++++++++++---
>  6 files changed, 32 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c 
> b/arch/powerpc/platforms/pseries/hotplug-memory.c
> index b3f54466e25f..2e6f41dc103a 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
> @@ -702,7 +702,7 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
>         nid = memory_add_physaddr_to_nid(lmb->base_addr);
>
>         /* Add the memory */
> -       rc = add_memory(nid, lmb->base_addr, block_sz);
> +       rc = __add_memory(nid, lmb->base_addr, block_sz);
>         if (rc) {
>                 dlpar_remove_device_tree_lmb(lmb);
>                 return rc;
> diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
> index 811148415993..8fe0960ea572 100644
> --- a/drivers/acpi/acpi_memhotplug.c
> +++ b/drivers/acpi/acpi_memhotplug.c
> @@ -228,7 +228,7 @@ static int acpi_memory_enable_device(struct 
> acpi_memory_device *mem_device)
>                 if (node < 0)
>                         node = memory_add_physaddr_to_nid(info->start_addr);
>
> -               result = add_memory(node, info->start_addr, info->length);
> +               result = __add_memory(node, info->start_addr, info->length);
>
>                 /*
>                  * If the memory block has been used by the kernel, 
> add_memory()
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 817320c7c4c1..40cac122ec73 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -519,15 +519,20 @@ memory_probe_store(struct device *dev, struct 
> device_attribute *attr,
>         if (phys_addr & ((pages_per_block << PAGE_SHIFT) - 1))
>                 return -EINVAL;
>
> +       ret = lock_device_hotplug_sysfs();
> +       if (ret)
> +               goto out;
> +
>         nid = memory_add_physaddr_to_nid(phys_addr);
> -       ret = add_memory(nid, phys_addr,
> -                        MIN_MEMORY_BLOCK_SIZE * sections_per_block);
> +       ret = __add_memory(nid, phys_addr,
> +                          MIN_MEMORY_BLOCK_SIZE * sections_per_block);
>
>         if (ret)
>                 goto out;
>
>         ret = count;
>  out:
> +       unlock_device_hotplug();
>         return ret;
>  }
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index e12bb256036f..6bab019a82b1 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -395,7 +395,10 @@ static enum bp_state reserve_additional_memory(void)
>          * callers drop the mutex before trying again.
>          */
>         mutex_unlock(&balloon_mutex);
> +       /* add_memory_resource() requires the device_hotplug lock */
> +       lock_device_hotplug();
>         rc = add_memory_resource(nid, resource, memhp_auto_online);
> +       unlock_device_hotplug();
>         mutex_lock(&balloon_mutex);
>
>         if (rc) {
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 1f096852f479..ffd9cd10fcf3 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -324,6 +324,7 @@ static inline void __remove_memory(int nid, u64 start, 
> u64 size) {}
>  extern void __ref free_area_init_core_hotplug(int nid);
>  extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
>                 void *arg, int (*func)(struct memory_block *, void *));
> +extern int __add_memory(int nid, u64 start, u64 size);
>  extern int add_memory(int nid, u64 start, u64 size);
>  extern int add_memory_resource(int nid, struct resource *resource, bool 
> online);
>  extern int arch_add_memory(int nid, u64 start, u64 size,
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b8b1bd970322..ef5444145c88 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1111,7 +1111,12 @@ static int online_memory_block(struct memory_block 
> *mem, void *arg)
>         return device_online(&mem->dev);
>  }
>
> -/* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
> +/*
> + * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
> + * and online/offline operations (triggered e.g. by sysfs).
> + *
> + * we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG
> + */
>  int __ref add_memory_resource(int nid, struct resource *res, bool online)
>  {
>         u64 start, size;
> @@ -1180,9 +1185,9 @@ int __ref add_memory_resource(int nid, struct resource 
> *res, bool online)
>         mem_hotplug_done();
>         return ret;
>  }
> -EXPORT_SYMBOL_GPL(add_memory_resource);
>
> -int __ref add_memory(int nid, u64 start, u64 size)
> +/* requires device_hotplug_lock, see add_memory_resource() */
> +int __ref __add_memory(int nid, u64 start, u64 size)
>  {
>         struct resource *res;
>         int ret;
> @@ -1196,6 +1201,17 @@ int __ref add_memory(int nid, u64 start, u64 size)
>                 release_memory_resource(res);
>         return ret;
>  }
> +
> +int add_memory(int nid, u64 start, u64 size)
> +{
> +       int rc;
> +
> +       lock_device_hotplug();
> +       rc = __add_memory(nid, start, size);
> +       unlock_device_hotplug();
> +
> +       return rc;
> +}
>  EXPORT_SYMBOL_GPL(add_memory);
>
>  #ifdef CONFIG_MEMORY_HOTREMOVE
> --

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

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