Re: [PATCH v2 3/3] mm: don't panic when links can't be created in sysfs

David Hildenbrand
2020-09-15T07:23:49Z

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