Date:   Mon, 1 Jul 2019 10:14:20 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, akpm@...ux-foundation.org,
        Dan Williams <dan.j.williams@...el.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "mike.travis@....com" <mike.travis@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Banman <andrew.banman@....com>,
        Oscar Salvador <osalvador@...e.de>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Qian Cai <cai@....pw>, Arun KS <arunks@...eaurora.org>,
        Mathieu Malaterre <malat@...ian.org>
Subject: Re: [PATCH v3 07/11] mm/memory_hotplug: Create memory block devices
 after arch_add_memory()

On Mon 27-05-19 13:11:48, David Hildenbrand wrote:
> Only memory to be added to the buddy and to be onlined/offlined by
> user space using /sys/devices/system/memory/... needs (and should have!)
> memory block devices.
> 
> Factor out creation of memory block devices. Create all devices after
> arch_add_memory() succeeded. We can later drop the want_memblock parameter,
> because it is now effectively stale.
> 
> Only after memory block devices have been added, memory can be onlined
> by user space. This implies, that memory is not visible to user space at
> all before arch_add_memory() succeeded.

I like the memblock API to go away from the low level hotplug handling.
The current implementation is just too convoluted and I remember I was
fighting with subtle expectations wired deep in call chains when
touching that code in the past (some memblocks didn't get created etc.).
Maybe those have been addressed in the meantime.

> While at it
> - use WARN_ON_ONCE instead of BUG_ON in moved unregister_memory()

This would better be a separate patch with an explanation

> - introduce find_memory_block_by_id() to search via block id
> - Use find_memory_block_by_id() in init_memory_block() to catch
>   duplicates
> 
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: "mike.travis@....com" <mike.travis@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Andrew Banman <andrew.banman@....com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Pavel Tatashin <pasha.tatashin@...een.com>
> Cc: Qian Cai <cai@....pw>
> Cc: Wei Yang <richard.weiyang@...il.com>
> Cc: Arun KS <arunks@...eaurora.org>
> Cc: Mathieu Malaterre <malat@...ian.org>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Other than that looks good to me.
Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  drivers/base/memory.c  | 82 +++++++++++++++++++++++++++---------------
>  include/linux/memory.h |  2 +-
>  mm/memory_hotplug.c    | 15 ++++----
>  3 files changed, 63 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index ac17c95a5f28..5a0370f0c506 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -39,6 +39,11 @@ static inline int base_memory_block_id(int section_nr)
>  	return section_nr / sections_per_block;
>  }
>  
> +static inline int pfn_to_block_id(unsigned long pfn)
> +{
> +	return base_memory_block_id(pfn_to_section_nr(pfn));
> +}
> +
>  static int memory_subsys_online(struct device *dev);
>  static int memory_subsys_offline(struct device *dev);
>  
> @@ -582,10 +587,9 @@ int __weak arch_get_memory_phys_device(unsigned long start_pfn)
>   * A reference for the returned object is held and the reference for the
>   * hinted object is released.
>   */
> -struct memory_block *find_memory_block_hinted(struct mem_section *section,
> -					      struct memory_block *hint)
> +static struct memory_block *find_memory_block_by_id(int block_id,
> +						    struct memory_block *hint)
>  {
> -	int block_id = base_memory_block_id(__section_nr(section));
>  	struct device *hintdev = hint ? &hint->dev : NULL;
>  	struct device *dev;
>  
> @@ -597,6 +601,14 @@ struct memory_block *find_memory_block_hinted(struct mem_section *section,
>  	return to_memory_block(dev);
>  }
>  
> +struct memory_block *find_memory_block_hinted(struct mem_section *section,
> +					      struct memory_block *hint)
> +{
> +	int block_id = base_memory_block_id(__section_nr(section));
> +
> +	return find_memory_block_by_id(block_id, hint);
> +}
> +
>  /*
>   * For now, we have a linear search to go find the appropriate
>   * memory_block corresponding to a particular phys_index. If
> @@ -658,6 +670,11 @@ static int init_memory_block(struct memory_block **memory, int block_id,
>  	unsigned long start_pfn;
>  	int ret = 0;
>  
> +	mem = find_memory_block_by_id(block_id, NULL);
> +	if (mem) {
> +		put_device(&mem->dev);
> +		return -EEXIST;
> +	}
>  	mem = kzalloc(sizeof(*mem), GFP_KERNEL);
>  	if (!mem)
>  		return -ENOMEM;
> @@ -699,44 +716,53 @@ static int add_memory_block(int base_section_nr)
>  	return 0;
>  }
>  
> +static void unregister_memory(struct memory_block *memory)
> +{
> +	if (WARN_ON_ONCE(memory->dev.bus != &memory_subsys))
> +		return;
> +
> +	/* drop the ref. we got via find_memory_block() */
> +	put_device(&memory->dev);
> +	device_unregister(&memory->dev);
> +}
> +
>  /*
> - * need an interface for the VM to add new memory regions,
> - * but without onlining it.
> + * Create memory block devices for the given memory area. Start and size
> + * have to be aligned to memory block granularity. Memory block devices
> + * will be initialized as offline.
>   */
> -int hotplug_memory_register(int nid, struct mem_section *section)
> +int create_memory_block_devices(unsigned long start, unsigned long size)
>  {
> -	int block_id = base_memory_block_id(__section_nr(section));
> -	int ret = 0;
> +	const int start_block_id = pfn_to_block_id(PFN_DOWN(start));
> +	int end_block_id = pfn_to_block_id(PFN_DOWN(start + size));
>  	struct memory_block *mem;
> +	unsigned long block_id;
> +	int ret = 0;
>  
> -	mutex_lock(&mem_sysfs_mutex);
> +	if (WARN_ON_ONCE(!IS_ALIGNED(start, memory_block_size_bytes()) ||
> +			 !IS_ALIGNED(size, memory_block_size_bytes())))
> +		return -EINVAL;
>  
> -	mem = find_memory_block(section);
> -	if (mem) {
> -		mem->section_count++;
> -		put_device(&mem->dev);
> -	} else {
> +	mutex_lock(&mem_sysfs_mutex);
> +	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
>  		ret = init_memory_block(&mem, block_id, MEM_OFFLINE);
>  		if (ret)
> -			goto out;
> -		mem->section_count++;
> +			break;
> +		mem->section_count = sections_per_block;
> +	}
> +	if (ret) {
> +		end_block_id = block_id;
> +		for (block_id = start_block_id; block_id != end_block_id;
> +		     block_id++) {
> +			mem = find_memory_block_by_id(block_id, NULL);
> +			mem->section_count = 0;
> +			unregister_memory(mem);
> +		}
>  	}
> -
> -out:
>  	mutex_unlock(&mem_sysfs_mutex);
>  	return ret;
>  }
>  
> -static void
> -unregister_memory(struct memory_block *memory)
> -{
> -	BUG_ON(memory->dev.bus != &memory_subsys);
> -
> -	/* drop the ref. we got via find_memory_block() */
> -	put_device(&memory->dev);
> -	device_unregister(&memory->dev);
> -}
> -
>  void unregister_memory_section(struct mem_section *section)
>  {
>  	struct memory_block *mem;
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index 474c7c60c8f2..db3e8567f900 100644
> --- a/include/linux/memory.h
> +++ b/include/linux/memory.h
> @@ -111,7 +111,7 @@ extern int register_memory_notifier(struct notifier_block *nb);
>  extern void unregister_memory_notifier(struct notifier_block *nb);
>  extern int register_memory_isolate_notifier(struct notifier_block *nb);
>  extern void unregister_memory_isolate_notifier(struct notifier_block *nb);
> -int hotplug_memory_register(int nid, struct mem_section *section);
> +int create_memory_block_devices(unsigned long start, unsigned long size);
>  extern void unregister_memory_section(struct mem_section *);
>  extern int memory_dev_init(void);
>  extern int memory_notify(unsigned long val, void *v);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 4b9d2974f86c..b1fde90bbf19 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -259,13 +259,7 @@ static int __meminit __add_section(int nid, unsigned long phys_start_pfn,
>  		return -EEXIST;
>  
>  	ret = sparse_add_one_section(nid, phys_start_pfn, altmap);
> -	if (ret < 0)
> -		return ret;
> -
> -	if (!want_memblock)
> -		return 0;
> -
> -	return hotplug_memory_register(nid, __pfn_to_section(phys_start_pfn));
> +	return ret < 0 ? ret : 0;
>  }
>  
>  /*
> @@ -1107,6 +1101,13 @@ int __ref add_memory_resource(int nid, struct resource *res)
>  	if (ret < 0)
>  		goto error;
>  
> +	/* create memory block devices after memory was added */
> +	ret = create_memory_block_devices(start, size);
> +	if (ret) {
> +		arch_remove_memory(nid, start, size, NULL);
> +		goto error;
> +	}
> +
>  	if (new_node) {
>  		/* If sysfs file of new node can't be created, cpu on the node
>  		 * can't be hot-added. There is no rollback way now.
> -- 
> 2.20.1
> 

-- 
Michal Hocko
SUSE Labs

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