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Subject: Re: [PATCH v2 3/3] mm: don't panic when links can't be created in
 sysfs
To:     Laurent Dufour <ldufour@linux.ibm.com>, akpm@linux-foundation.org,
        Oscar Salvador <osalvador@suse.de>, mhocko@kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-mm@kvack.org, "Rafael J . Wysocki" <rafael@kernel.org>,
        nathanl@linux.ibm.com, cheloha@linux.ibm.com,
        Tony Luck <tony.luck@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>, linux-ia64@vger.kernel.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Michal Hocko <mhocko@suse.com>
References: <20200914165042.96218-1-ldufour@linux.ibm.com>
 <20200914165042.96218-4-ldufour@linux.ibm.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <a62d5cde-85c9-8650-d5e0-d277c6f7360f@redhat.com>
Date:   Tue, 15 Sep 2020 09:23:20 +0200
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On 14.09.20 18:50, Laurent Dufour wrote:
> At boot time, or when doing memory hot-add operations, if the links in
> sysfs can't be created, the system is still able to run, so just report the
> error in the kernel log rather than BUG_ON and potentially make system
> unusable because the callpath can be called with locks held.
> 
> Since the number of memory blocks managed could be high, the messages are
> rate limited.
> 
> As a consequence, link_mem_sections() has no status to report anymore.
> 
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/base/node.c  | 33 +++++++++++++++++++++------------
>  include/linux/node.h | 16 +++++++---------
>  mm/memory_hotplug.c  |  5 ++---
>  3 files changed, 30 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 01ee73c9d675..249b2ba6dc81 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -761,8 +761,8 @@ static int __ref get_nid_for_pfn(unsigned long pfn)
>  	return pfn_to_nid(pfn);
>  }
>  
> -static int do_register_memory_block_under_node(int nid,
> -					       struct memory_block *mem_blk)
> +static void do_register_memory_block_under_node(int nid,
> +						struct memory_block *mem_blk)
>  {
>  	int ret;
>  
> @@ -775,12 +775,19 @@ static int do_register_memory_block_under_node(int nid,
>  	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
>  				       &mem_blk->dev.kobj,
>  				       kobject_name(&mem_blk->dev.kobj));
> -	if (ret)
> -		return ret;
> +	if (ret && ret != -EEXIST)
> +		dev_err_ratelimited(&node_devices[nid]->dev,
> +				    "can't create link to %s in sysfs (%d)\n",
> +				    kobject_name(&mem_blk->dev.kobj), ret);
>  
> -	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
> +	ret = sysfs_create_link_nowarn(&mem_blk->dev.kobj,
>  				&node_devices[nid]->dev.kobj,
>  				kobject_name(&node_devices[nid]->dev.kobj));
> +	if (ret && ret != -EEXIST)
> +		dev_err_ratelimited(&mem_blk->dev,
> +				    "can't create link to %s in sysfs (%d)\n",
> +				    kobject_name(&node_devices[nid]->dev.kobj),
> +				    ret);
>  }
>  
>  /* register memory section under specified node if it spans that node */
> @@ -817,7 +824,8 @@ static int register_mem_block_under_node_early(struct memory_block *mem_blk,
>  			continue;
>  
>  		/* The memory block is registered to the first matching node */
> -		return do_register_memory_block_under_node(nid, mem_blk);
> +		do_register_memory_block_under_node(nid, mem_blk);
> +		return 0;
>  	}
>  	/* mem section does not span the specified node */
>  	return 0;
> @@ -832,7 +840,8 @@ static int register_mem_block_under_node_hotplug(struct memory_block *mem_blk,
>  {
>  	int nid = *(int *)arg;
>  
> -	return do_register_memory_block_under_node(nid, mem_blk);
> +	do_register_memory_block_under_node(nid, mem_blk);
> +	return 0;
>  }
>  
>  /*
> @@ -850,8 +859,8 @@ void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
>  			  kobject_name(&node_devices[mem_blk->nid]->dev.kobj));
>  }
>  
> -int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn,
> -		      enum meminit_context context)
> +void link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn,
> +		       enum meminit_context context)
>  {
>  	walk_memory_blocks_func_t func;
>  
> @@ -860,9 +869,9 @@ int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn,
>  	else
>  		func = register_mem_block_under_node_early;
>  
> -	return walk_memory_blocks(PFN_PHYS(start_pfn),
> -				  PFN_PHYS(end_pfn - start_pfn), (void *)&nid,
> -				  func);
> +	walk_memory_blocks(PFN_PHYS(start_pfn), PFN_PHYS(end_pfn - start_pfn),
> +			   (void *)&nid, func);
> +	return;
>  }
>  
>  #ifdef CONFIG_HUGETLBFS
> diff --git a/include/linux/node.h b/include/linux/node.h
> index 014ba3ab2efd..8e5a29897936 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -99,15 +99,14 @@ extern struct node *node_devices[];
>  typedef  void (*node_registration_func_t)(struct node *);
>  
>  #if defined(CONFIG_MEMORY_HOTPLUG_SPARSE) && defined(CONFIG_NUMA)
> -int link_mem_sections(int nid, unsigned long start_pfn,
> -		      unsigned long end_pfn,
> -		      enum meminit_context context);
> +void link_mem_sections(int nid, unsigned long start_pfn,
> +		       unsigned long end_pfn,
> +		       enum meminit_context context);
>  #else
> -static inline int link_mem_sections(int nid, unsigned long start_pfn,
> -				    unsigned long end_pfn,
> -				    enum meminit_context context)
> +static inline void link_mem_sections(int nid, unsigned long start_pfn,
> +				     unsigned long end_pfn,
> +				     enum meminit_context context)
>  {
> -	return 0;
>  }
>  #endif
>  
> @@ -130,8 +129,7 @@ static inline int register_one_node(int nid)
>  		if (error)
>  			return error;
>  		/* link memory sections under this node */
> -		error = link_mem_sections(nid, start_pfn, end_pfn,
> -					  MEMINIT_EARLY);
> +		link_mem_sections(nid, start_pfn, end_pfn, MEMINIT_EARLY);
>  	}
>  
>  	return error;
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 03df20078827..01e01a530d38 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1080,9 +1080,8 @@ int __ref add_memory_resource(int nid, struct resource *res)
>  	}
>  
>  	/* link memory sections under this node.*/
> -	ret = link_mem_sections(nid, PFN_DOWN(start), PFN_UP(start + size - 1),
> -				MEMINIT_HOTPLUG);
> -	BUG_ON(ret);
> +	link_mem_sections(nid, PFN_DOWN(start), PFN_UP(start + size - 1),
> +			  MEMINIT_HOTPLUG);
>  
>  	/* create new memmap entry */
>  	if (!strcmp(res->name, "System RAM"))
> 

I just remember that I still have some cleanup patches lying around that
rework the whole node onlining on the add_memory() path, being able to
fail in a nice way rather than ignoring errors. Anyhow, this is good
enough for now

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb